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8 <title>Glossary - Apache HTTP Server</title>
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14 <p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p>
15 <p class="apache">Apache HTTP Server Version 2.1</p>
16 <img alt="" src="./images/feather.gif" /></div>
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19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.1</a></div><div id="page-content"><div id="preamble"><h1>Glossary</h1>
21 <p><span>Available Languages: </span><a href="./en/glossary.html"> en </a> | <a href="./ko/glossary.html"> ko </a></p>
24 <p>This glossary defines some of the common terminology related to
25 Apache in particular, and web serving in general. More information
26 on each concept is provided in the links.</p>
28 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
30 <h2><a name="definitions" id="definitions">Definitions</a></h2>
33 <dt><a name="authentication">Authentication</a></dt> <dd>The positive
34 identification of a network entity such as a server, a client, or a
35 user.<br /> See: <a href="howto/auth.html">Authentication, Authorization, and Access
38 <dt><a name="accesscontrol">Access Control</a></dt>
39 <dd>The restriction of access to network realms. In an Apache context
40 usually the restriction of access to certain <em>URLs</em>.<br />
41 See: <a href="howto/auth.html">Authentication, Authorization, and Access
44 <dt><a name="algorithm">Algorithm</a></dt>
45 <dd>An unambiguous formula or set of rules for solving a problem in
46 a finite number of steps. Algorithms for encryption are usually called
47 <dfn>Ciphers</dfn>.</dd>
49 <dt><a name="apacheextensiontool">APache eXtension Tool</a> <a name="apxs">(apxs)</a></dt> <dd>A perl script that aids in compiling <a href="#module">module</a> sources into Dynamic Shared Objects (<a href="#dso">DSO</a>s) and helps install them in the Apache Web
50 server.<br /> See: <a href="programs/apxs.html">Manual Page: apxs</a></dd>
52 <dt><a name="certificate">Certificate</a></dt>
53 <dd>A data record used for authenticating network entities such
54 as a server or a client. A certificate contains X.509 information pieces
55 about its owner (called the subject) and the signing <em>Certificate
56 Authority</em> (called the issuer), plus the owner's public key and the
57 signature made by the CA. Network entities verify these signatures using
58 CA certificates.<br />
59 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
61 <dt><a name="certificationauthority">Certification Authority</a> <a name="ca">(CA)</a></dt> <dd>A trusted third party whose purpose is to
62 sign certificates for network entities it has authenticated using
63 secure means. Other network entities can check the signature to verify
64 that a CA has authenticated the bearer of a certificate.<br />
65 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
67 <dt><a name="certificatsigningrequest">Certificate Signing Request</a>
68 <a name="csr">(CSR)</a></dt> <dd>An unsigned certificate for
69 submission to a <em>Certification Authority</em>, which signs it with
70 the <em>Private Key</em> of their CA <em>Certificate</em>. Once the
71 CSR is signed, it becomes a real certificate.<br />
72 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
75 <dt><a name="cipher">Cipher</a></dt> <dd>An algorithm or system for
76 data encryption. Examples are DES, IDEA, RC4, etc.<br />
77 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
79 <dt><a name="ciphertext">Ciphertext</a></dt> <dd>The result after <a href="#plaintext">Plaintext</a> is passed through a <a href="#cipher">Cipher</a>.<br /> See: <a href="ssl/">SSL/TLS
82 <dt><a name="commongatewayinterface">Common Gateway Interface</a> <a name="cgi">(CGI)</a></dt> <dd>A standard definition for an interface
83 between a web server and an external program that allows the external
84 program to service requests. The interface was originally defined by
85 <a href="http://hoohoo.ncsa.uiuc.edu/cgi/overview.html">NCSA</a> but
86 there is also an <a href="http://cgi-spec.golux.com/">RFC
88 See: <a href="howto/cgi.html">Dynamic Content with CGI</a></dd>
91 <dt><a name="configurationdirective">Configuration Directive</a></dt>
92 <dd>See: <a href="#directive">Directive</a></dd>
94 <dt><a name="configurationfile">Configuration File</a></dt>
95 <dd>A text file containing <a href="#directive">Directives</a>
96 that control the configuration of Apache.<br />
97 See: <a href="configuring.html">Configuration Files</a></dd>
99 <dt><a name="connect">CONNECT</a></dt> <dd>An HTTP <a href="#method">method</a> for proxying raw data channels over HTTP. It
100 can be used to encapsulate other protocols, such as the SSL
103 <dt><a name="context">Context</a></dt> <dd>An area in the <a href="#configurationfile">configuration files</a> where certain types
104 of <a href="#directive">directives</a> are allowed.<br /> See: <a href="mod/directive-dict.html#Context">Terms
105 Used to Describe Apache Directives</a></dd>
107 <dt><a name="digitalsignature">Digital Signature</a></dt>
108 <dd>An encrypted text block that validates a certificate or other file. A
109 <em>Certification Authority</em> creates a signature by generating a
110 hash of the <em>Public Key</em> embedded in a <em>Certificate</em>, then
111 encrypting the hash with its own <em>Private Key</em>. Only the CA's
112 public key can decrypt the signature, verifying that the CA has
113 authenticated the network entity that owns the <em>Certificate</em>.<br />
114 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
116 <dt><a name="directive">Directive</a></dt> <dd>A configuration command
117 that controls one or more aspects of Apache's behavior. Directives
118 are placed in the <a href="#configurationfile">Configuration
119 File</a><br /> See: <a href="mod/directives.html">Directive
122 <dt><a name="dynamicsharedobject">Dynamic Shared Object</a> <a name="dso">(DSO)</a></dt> <dd><a href="#module">Modules</a> compiled
123 separately from the Apache httpd binary that can be loaded on-demand.<br />
124 See: <a href="dso.html">Dynamic Shared Object Support</a></dd>
126 <dt><a name="environmentvariable">Environment Variable</a> <a name="env-variable">(env-variable)</a></dt>
127 <dd>Named variables managed by the operating system shell
128 and used to store information and communicate between programs. Apache also
129 contains internal variables that are referred to as environment variables,
130 but are stored in internal Apache structures, rather than in the
131 shell environment.<br />
132 See: <a href="env.html">Environment Variables in Apache</a></dd>
134 <dt><a name="export-crippled">Export-Crippled</a></dt>
135 <dd>Diminished in cryptographic strength (and security) in order to comply
136 with the United States' Export Administration Regulations (EAR).
137 Export-crippled cryptographic software is limited to a small key size,
138 resulting in <em>Ciphertext</em> which usually can be decrypted by brute
140 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
142 <dt><a name="filter">Filter</a></dt> <dd>A process that is applied to
143 data that is sent or received by the server. Input filters process
144 data sent by the client to the server, while output filters process
145 documents on the server before they are sent to the client. For
146 example, the <code>INCLUDES</code> output filter processes documents
147 for <a href="#ssi">Server Side Includes</a>.<br /> See: <a href="filter.html">Filters</a></dd>
149 <dt><a name="fully-qualifieddomain-name">Fully-Qualified
150 Domain-Name</a> <a name="fqdn">(FQDN)</a></dt> <dd>The unique name of
151 a network entity, consisting of a hostname and a domain name that can
152 resolve to an IP address. For example, <code>www</code> is a hostname,
153 <code>example.com</code> is a domain name, and
154 <code>www.example.com</code> is a fully-qualified domain name.</dd>
156 <dt><a name="handler">Handler</a></dt> <dd>An internal Apache
157 representation of the action to be performed when a file is
158 called. Generally, files have implicit handlers, based on the file
159 type. Normally, all files are simply served by the server, but certain
160 file types are "handled" separately. For example, the
161 <code>cgi-script</code> handler designates files to be processed as <a href="#cgi">CGIs</a>.<br />
162 See: <a href="handler.html">Apache's Handler Use</a></dd>
164 <dt><a name="header">Header</a></dt>
165 <dd>The part of the <a href="#http">HTTP</a> request and response that
166 is sent before the actual content, and that contains meta-information
167 describing the content.</dd>
169 <dt><a name=".htaccess">.htaccess</a></dt> <dd>A <a href="#configurationfile">configuration file</a> that is placed inside
170 the web tree and applies configuration <a href="#directive">directives</a> to the directory where it is placed
171 and all sub-directories. Despite its name, this file can hold almost
172 any type of directive, not just access-control directives.<br />
173 See: <a href="configuring.html">Configuration Files</a></dd>
175 <dt><a name="httpd.conf">httpd.conf</a></dt>
176 <dd>The main Apache <a href="#configurationfile">configuration file</a>.
177 The default location is <code>/usr/local/apache2/conf/httpd.conf</code>,
178 but it may be moved using run-time or compile-time configuration.<br />
179 See: <a href="configuring.html">Configuration Files</a></dd>
181 <dt><a name="hypertexttransferprotocol">HyperText Transfer
182 Protocol</a> <a name="http">(HTTP)</a></dt> <dd>The standard
183 transmission protocol used on the World Wide Web. Apache implements
184 version 1.1 of the protocol, referred to as HTTP/1.1 and defined by <a href="http://ietf.org/rfc/rfc2616.txt">RFC 2616</a>.</dd>
186 <dt><a name="https">HTTPS</a></dt>
187 <dd>The HyperText Transport Protocol (Secure), the standard encrypted
188 communication mechanism on the World Wide Web. This is actually just HTTP
189 over <a name="ssl">SSL</a>.<br />
190 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
192 <dt><a name="method">Method</a></dt> <dd>In the context of <a href="#http">HTTP</a>, an action to perform on a resource, specified
193 on the request line by the client. Some of the methods available in
194 HTTP are <code>GET</code>, <code>POST</code>, and <code>PUT</code>.</dd>
196 <dt><a name="messagedigest">Message Digest</a></dt>
197 <dd>A hash of a message, which can be used to verify that the contents of
198 the message have not been altered in transit.<br />
199 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
201 <dt><a name="mime-type">MIME-type</a></dt> <dd>A way to describe the
202 kind of document being transmitted. Its name comes from that fact
203 that its format is borrowed from the Multipurpose Internet Mail
204 Extensions. It consists of a major type and a minor type, separated
205 by a slash. Some examples are <code>text/html</code>,
206 <code>image/gif</code>, and <code>application/octet-stream</code>. In
207 HTTP, the MIME-type is transmitted in the <code>Content-Type</code> <a href="#header">header</a>.<br /> See: <a href="mod/mod_mime.html">mod_mime</a></dd>
209 <dt><a name="module">Module</a></dt> <dd>An independent part of a
210 program. Much of Apache's functionality is contained in modules that
211 you can choose to include or exclude. Modules that are compiled into
212 the Apache httpd binary are called <em>static modules</em>, while
213 modules that are stored separately and can be optionally loaded at
214 run-time are called <em>dynamic modules</em> or <a href="#dso">DSOs</a>. Modules that are included by default are called
215 <em>base modules</em>. Many modules are available for Apache that are
216 not distributed as part of the Apache HTTP Server <a href="#tarball">tarball</a>. These are referred to as <em>third-party
218 See: <a href="mod/">Module Index</a></dd>
220 <dt><a name="modulemagicnumber">Module Magic Number</a> (<a name="mmn">MMN</a>)</dt>
222 Module Magic Number is a constant defined in the Apache source code
223 that is associated with binary compatibility of modules. It is changed
224 when internal Apache structures, function calls and other significant
225 parts of API change in such a way that binary compatibility cannot be
226 guaranteed any more. On MMN change, all third party modules have to be
227 at least recompiled, sometimes even slightly changed in order to work
228 with the new version of Apache.
231 <dt><a name="openssl">OpenSSL</a></dt>
232 <dd>The Open Source toolkit for SSL/TLS<br />
233 see <a href="http://www.openssl.org/">http://www.openssl.org/</a></dd>
235 <dt><a name="passphrase">Pass Phrase</a></dt> <dd>The word or phrase
236 that protects private key files. It prevents unauthorized users from
237 encrypting them. Usually it's just the secret encryption/decryption
238 key used for <a name="cipher">Ciphers</a>.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
240 <dt><a name="plaintext">Plaintext</a></dt>
241 <dd>The unencrypted text.</dd>
243 <dt><a name="privatekey">Private Key</a></dt> <dd>The secret key in a
244 <a name="publickeycryptography">Public Key Cryptography</a> system,
245 used to decrypt incoming messages and sign outgoing ones.<br />
246 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
248 <dt><a name="proxy">Proxy</a></dt> <dd>An intermediate server that
249 sits between the client and the <em>origin server</em>. It accepts
250 requests from clients, transmits those requests on to the origin
251 server, and then returns the response from the origin server to the
252 client. If several clients request the same content, the proxy
253 can deliver that content from its cache, rather than requesting it
254 from the origin server each time, thereby reducing response time.<br />
255 See: <a href="mod/mod_proxy.html">mod_proxy</a></dd>
257 <dt><a name="publickey">Public Key</a></dt> <dd>The publicly
258 available key in a <a name="publickeycryptography">Public Key
259 Cryptography</a> system, used to encrypt messages bound for its owner
260 and to decrypt signatures made by its owner.<br />
261 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
263 <dt><a name="publickeycryptography">Public Key Cryptography</a></dt>
264 <dd>The study and application of asymmetric encryption systems, which
265 use one key for encryption and another for decryption. A corresponding
266 pair of such keys constitutes a key pair. Also called Asymmetric
267 Cryptography.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
269 <dt><a name="regularexpresion">Regular Expression</a> <a name="regex">(Regex)</a></dt> <dd>A way of
270 describing a pattern in text - for example, "all the words that begin with the
271 letter A" or "every 10-digit phone number" or even "Every sentence
272 with two commas in it, and no capital letter Q". Regular expressions
273 are useful in Apache because they let you apply certain
274 attributes against collections of files or resources in very flexible
275 ways - for example, all .gif and .jpg files under any "images"
276 directory could be written as "<code>/images/.*(jpg|gif)$</code>".
277 Apache uses Perl Compatible Regular Expressions provided by the
278 <a href="http://www.pcre.org/">PCRE</a> library.</dd>
280 <dt><a name="reverseproxy">Reverse Proxy</a></dt> <dd>A <a href="#proxy">proxy</a> server that appears to the client as if it is
281 an <em>origin server</em>. This is useful to hide the real origin
282 server from the client for security reasons, or to load balance.</dd>
284 <dt><a name="securesocketslayer">Secure Sockets Layer</a> <a name="ssl">(SSL)</a></dt> <dd>A protocol created by Netscape
285 Communications Corporation for general communication authentication
286 and encryption over TCP/IP networks. The most popular usage is
287 <em>HTTPS</em>, i.e. the HyperText Transfer Protocol (HTTP) over SSL.<br />
288 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
290 <dt><a name="serversideincludes">Server Side Includes</a> <a name="ssi">(SSI)</a></dt> <dd>A technique for embedding processing
291 directives inside HTML files.<br /> See: <a href="howto/ssi.html">Introduction to Server Side Includes</a></dd>
293 <dt><a name="session">Session</a></dt>
294 <dd>The context information of a communication in general.</dd>
296 <dt><a name="ssleay">SSLeay</a></dt>
297 <dd>The original SSL/TLS implementation library developed by
300 <dt><a name="symmetriccryptophraphy">Symmetric Cryptography</a></dt>
301 <dd>The study and application of <em>Ciphers</em> that use a single secret key
302 for both encryption and decryption operations.<br />
303 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
305 <dt><a name="tarball">Tarball</a></dt>
306 <dd>A package of files gathered together using the <code>tar</code>
307 utility. Apache distributions are stored in compressed tar archives
310 <dt><a name="transportlayersecurity">Transport Layer Security</a> <a name="tls">(TLS)</a></dt> <dd>The successor protocol to SSL, created
311 by the Internet Engineering Task Force (IETF) for general
312 communication authentication and encryption over TCP/IP networks. TLS
313 version 1 and is nearly identical with SSL version 3.<br />
314 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
316 <dt><a name="uniformresourcelocator">Uniform Resource Locator</a> <a name="url">(URL)</a></dt> <dd>The name/address of a resource on the
317 Internet. This is the common informal term for what is formally
318 called a <a href="#uniformresourceidentifier">Uniform Resource
319 Identifier</a>. URLs are usually made up of a scheme, like
320 <code>http</code> or <code>https</code>, a hostname, and a path. A
322 <code>http://httpd.apache.org/docs-2.1/glossary.html</code>.</dd>
324 <dt><a name="uniformresourceidentifier">Uniform Resource Identifier</a> <a name="URI">(URI)</a></dt> <dd>A compact string of characters for
325 identifying an abstract or physical resource. It is formally defined
326 by <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>.
327 URIs used on the world-wide web are commonly referred to
328 as <a href="#url">URLs</a>.</dd>
330 <dt><a name="virtualhosting">Virtual Hosting</a></dt> <dd>Serving
331 multiple websites using a single instance of Apache. <em>IP virtual
332 hosting</em> differentiates between websites based on their IP
333 address, while <em>name-based virtual hosting</em> uses only the name
334 of the host and can therefore host many sites on the same IP
335 address.<br /> See: <a href="vhosts/">Apache Virtual Host
336 documentation</a></dd>
338 <dt><a name="x.509">X.509</a></dt> <dd>An authentication certificate
339 scheme recommended by the International Telecommunication Union
340 (ITU-T) which is used for SSL/TLS authentication.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
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