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8 <title>Glossary - Apache HTTP Server</title>
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15 <p class="apache">Apache HTTP Server Version 2.1</p>
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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" title="English"> en </a> |
22 <a href="./ko/glossary.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
25 <p>This glossary defines some of the common terminology related to
26 Apache in particular, and web serving in general. More information
27 on each concept is provided in the links.</p>
29 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
31 <h2><a name="definitions" id="definitions">Definitions</a></h2>
34 <dt><a name="authentication">Authentication</a></dt> <dd>The positive
35 identification of a network entity such as a server, a client, or a
36 user.<br /> See: <a href="howto/auth.html">Authentication, Authorization, and Access
39 <dt><a name="accesscontrol">Access Control</a></dt>
40 <dd>The restriction of access to network realms. In an Apache context
41 usually the restriction of access to certain <em>URLs</em>.<br />
42 See: <a href="howto/auth.html">Authentication, Authorization, and Access
45 <dt><a name="algorithm">Algorithm</a></dt>
46 <dd>An unambiguous formula or set of rules for solving a problem in
47 a finite number of steps. Algorithms for encryption are usually called
48 <dfn>Ciphers</dfn>.</dd>
50 <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
51 server.<br /> See: <a href="programs/apxs.html">Manual Page: apxs</a></dd>
53 <dt><a name="certificate">Certificate</a></dt>
54 <dd>A data record used for authenticating network entities such
55 as a server or a client. A certificate contains X.509 information pieces
56 about its owner (called the subject) and the signing <em>Certificate
57 Authority</em> (called the issuer), plus the owner's public key and the
58 signature made by the CA. Network entities verify these signatures using
59 CA certificates.<br />
60 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
62 <dt><a name="certificationauthority">Certification Authority</a> <a name="ca">(CA)</a></dt> <dd>A trusted third party whose purpose is to
63 sign certificates for network entities it has authenticated using
64 secure means. Other network entities can check the signature to verify
65 that a CA has authenticated the bearer of a certificate.<br />
66 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
68 <dt><a name="certificatsigningrequest">Certificate Signing Request</a>
69 <a name="csr">(CSR)</a></dt> <dd>An unsigned certificate for
70 submission to a <em>Certification Authority</em>, which signs it with
71 the <em>Private Key</em> of their CA <em>Certificate</em>. Once the
72 CSR is signed, it becomes a real certificate.<br />
73 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
76 <dt><a name="cipher">Cipher</a></dt> <dd>An algorithm or system for
77 data encryption. Examples are DES, IDEA, RC4, etc.<br />
78 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
80 <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
83 <dt><a name="commongatewayinterface">Common Gateway Interface</a> <a name="cgi">(CGI)</a></dt> <dd>A standard definition for an interface
84 between a web server and an external program that allows the external
85 program to service requests. The interface was originally defined by
86 <a href="http://hoohoo.ncsa.uiuc.edu/cgi/overview.html">NCSA</a> but
87 there is also an <a href="http://cgi-spec.golux.com/">RFC
89 See: <a href="howto/cgi.html">Dynamic Content with CGI</a></dd>
92 <dt><a name="configurationdirective">Configuration Directive</a></dt>
93 <dd>See: <a href="#directive">Directive</a></dd>
95 <dt><a name="configurationfile">Configuration File</a></dt>
96 <dd>A text file containing <a href="#directive">Directives</a>
97 that control the configuration of Apache.<br />
98 See: <a href="configuring.html">Configuration Files</a></dd>
100 <dt><a name="connect">CONNECT</a></dt> <dd>An HTTP <a href="#method">method</a> for proxying raw data channels over HTTP. It
101 can be used to encapsulate other protocols, such as the SSL
104 <dt><a name="context">Context</a></dt> <dd>An area in the <a href="#configurationfile">configuration files</a> where certain types
105 of <a href="#directive">directives</a> are allowed.<br /> See: <a href="mod/directive-dict.html#Context">Terms
106 Used to Describe Apache Directives</a></dd>
108 <dt><a name="digitalsignature">Digital Signature</a></dt>
109 <dd>An encrypted text block that validates a certificate or other file. A
110 <em>Certification Authority</em> creates a signature by generating a
111 hash of the <em>Public Key</em> embedded in a <em>Certificate</em>, then
112 encrypting the hash with its own <em>Private Key</em>. Only the CA's
113 public key can decrypt the signature, verifying that the CA has
114 authenticated the network entity that owns the <em>Certificate</em>.<br />
115 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
117 <dt><a name="directive">Directive</a></dt> <dd>A configuration command
118 that controls one or more aspects of Apache's behavior. Directives
119 are placed in the <a href="#configurationfile">Configuration
120 File</a><br /> See: <a href="mod/directives.html">Directive
123 <dt><a name="dynamicsharedobject">Dynamic Shared Object</a> <a name="dso">(DSO)</a></dt> <dd><a href="#module">Modules</a> compiled
124 separately from the Apache httpd binary that can be loaded on-demand.<br />
125 See: <a href="dso.html">Dynamic Shared Object Support</a></dd>
127 <dt><a name="environmentvariable">Environment Variable</a> <a name="env-variable">(env-variable)</a></dt>
128 <dd>Named variables managed by the operating system shell
129 and used to store information and communicate between programs. Apache also
130 contains internal variables that are referred to as environment variables,
131 but are stored in internal Apache structures, rather than in the
132 shell environment.<br />
133 See: <a href="env.html">Environment Variables in Apache</a></dd>
135 <dt><a name="export-crippled">Export-Crippled</a></dt>
136 <dd>Diminished in cryptographic strength (and security) in order to comply
137 with the United States' Export Administration Regulations (EAR).
138 Export-crippled cryptographic software is limited to a small key size,
139 resulting in <em>Ciphertext</em> which usually can be decrypted by brute
141 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
143 <dt><a name="filter">Filter</a></dt> <dd>A process that is applied to
144 data that is sent or received by the server. Input filters process
145 data sent by the client to the server, while output filters process
146 documents on the server before they are sent to the client. For
147 example, the <code>INCLUDES</code> output filter processes documents
148 for <a href="#ssi">Server Side Includes</a>.<br /> See: <a href="filter.html">Filters</a></dd>
150 <dt><a name="fully-qualifieddomain-name">Fully-Qualified
151 Domain-Name</a> <a name="fqdn">(FQDN)</a></dt> <dd>The unique name of
152 a network entity, consisting of a hostname and a domain name that can
153 resolve to an IP address. For example, <code>www</code> is a hostname,
154 <code>example.com</code> is a domain name, and
155 <code>www.example.com</code> is a fully-qualified domain name.</dd>
157 <dt><a name="handler">Handler</a></dt> <dd>An internal Apache
158 representation of the action to be performed when a file is
159 called. Generally, files have implicit handlers, based on the file
160 type. Normally, all files are simply served by the server, but certain
161 file types are "handled" separately. For example, the
162 <code>cgi-script</code> handler designates files to be processed as <a href="#cgi">CGIs</a>.<br />
163 See: <a href="handler.html">Apache's Handler Use</a></dd>
165 <dt><a name="header">Header</a></dt>
166 <dd>The part of the <a href="#http">HTTP</a> request and response that
167 is sent before the actual content, and that contains meta-information
168 describing the content.</dd>
170 <dt><a name=".htaccess">.htaccess</a></dt> <dd>A <a href="#configurationfile">configuration file</a> that is placed inside
171 the web tree and applies configuration <a href="#directive">directives</a> to the directory where it is placed
172 and all sub-directories. Despite its name, this file can hold almost
173 any type of directive, not just access-control directives.<br />
174 See: <a href="configuring.html">Configuration Files</a></dd>
176 <dt><a name="httpd.conf">httpd.conf</a></dt>
177 <dd>The main Apache <a href="#configurationfile">configuration file</a>.
178 The default location is <code>/usr/local/apache2/conf/httpd.conf</code>,
179 but it may be moved using run-time or compile-time configuration.<br />
180 See: <a href="configuring.html">Configuration Files</a></dd>
182 <dt><a name="hypertexttransferprotocol">HyperText Transfer
183 Protocol</a> <a name="http">(HTTP)</a></dt> <dd>The standard
184 transmission protocol used on the World Wide Web. Apache implements
185 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>
187 <dt><a name="https">HTTPS</a></dt>
188 <dd>The HyperText Transport Protocol (Secure), the standard encrypted
189 communication mechanism on the World Wide Web. This is actually just HTTP
190 over <a name="ssl">SSL</a>.<br />
191 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
193 <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
194 on the request line by the client. Some of the methods available in
195 HTTP are <code>GET</code>, <code>POST</code>, and <code>PUT</code>.</dd>
197 <dt><a name="messagedigest">Message Digest</a></dt>
198 <dd>A hash of a message, which can be used to verify that the contents of
199 the message have not been altered in transit.<br />
200 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
202 <dt><a name="mime-type">MIME-type</a></dt> <dd>A way to describe the
203 kind of document being transmitted. Its name comes from that fact
204 that its format is borrowed from the Multipurpose Internet Mail
205 Extensions. It consists of a major type and a minor type, separated
206 by a slash. Some examples are <code>text/html</code>,
207 <code>image/gif</code>, and <code>application/octet-stream</code>. In
208 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>
210 <dt><a name="module">Module</a></dt> <dd>An independent part of a
211 program. Much of Apache's functionality is contained in modules that
212 you can choose to include or exclude. Modules that are compiled into
213 the Apache httpd binary are called <em>static modules</em>, while
214 modules that are stored separately and can be optionally loaded at
215 run-time are called <em>dynamic modules</em> or <a href="#dso">DSOs</a>. Modules that are included by default are called
216 <em>base modules</em>. Many modules are available for Apache that are
217 not distributed as part of the Apache HTTP Server <a href="#tarball">tarball</a>. These are referred to as <em>third-party
219 See: <a href="mod/">Module Index</a></dd>
221 <dt><a name="modulemagicnumber">Module Magic Number</a> (<a name="mmn">MMN</a>)</dt>
223 Module Magic Number is a constant defined in the Apache source code
224 that is associated with binary compatibility of modules. It is changed
225 when internal Apache structures, function calls and other significant
226 parts of API change in such a way that binary compatibility cannot be
227 guaranteed any more. On MMN change, all third party modules have to be
228 at least recompiled, sometimes even slightly changed in order to work
229 with the new version of Apache.
232 <dt><a name="openssl">OpenSSL</a></dt>
233 <dd>The Open Source toolkit for SSL/TLS<br />
234 see <a href="http://www.openssl.org/">http://www.openssl.org/</a></dd>
236 <dt><a name="passphrase">Pass Phrase</a></dt> <dd>The word or phrase
237 that protects private key files. It prevents unauthorized users from
238 encrypting them. Usually it's just the secret encryption/decryption
239 key used for <a name="cipher">Ciphers</a>.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
241 <dt><a name="plaintext">Plaintext</a></dt>
242 <dd>The unencrypted text.</dd>
244 <dt><a name="privatekey">Private Key</a></dt> <dd>The secret key in a
245 <a name="publickeycryptography">Public Key Cryptography</a> system,
246 used to decrypt incoming messages and sign outgoing ones.<br />
247 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
249 <dt><a name="proxy">Proxy</a></dt> <dd>An intermediate server that
250 sits between the client and the <em>origin server</em>. It accepts
251 requests from clients, transmits those requests on to the origin
252 server, and then returns the response from the origin server to the
253 client. If several clients request the same content, the proxy
254 can deliver that content from its cache, rather than requesting it
255 from the origin server each time, thereby reducing response time.<br />
256 See: <a href="mod/mod_proxy.html">mod_proxy</a></dd>
258 <dt><a name="publickey">Public Key</a></dt> <dd>The publicly
259 available key in a <a name="publickeycryptography">Public Key
260 Cryptography</a> system, used to encrypt messages bound for its owner
261 and to decrypt signatures made by its owner.<br />
262 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
264 <dt><a name="publickeycryptography">Public Key Cryptography</a></dt>
265 <dd>The study and application of asymmetric encryption systems, which
266 use one key for encryption and another for decryption. A corresponding
267 pair of such keys constitutes a key pair. Also called Asymmetric
268 Cryptography.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
270 <dt><a name="regularexpresion">Regular Expression</a> <a name="regex">(Regex)</a></dt> <dd>A way of
271 describing a pattern in text - for example, "all the words that begin with the
272 letter A" or "every 10-digit phone number" or even "Every sentence
273 with two commas in it, and no capital letter Q". Regular expressions
274 are useful in Apache because they let you apply certain
275 attributes against collections of files or resources in very flexible
276 ways - for example, all .gif and .jpg files under any "images"
277 directory could be written as "<code>/images/.*(jpg|gif)$</code>".
278 Apache uses Perl Compatible Regular Expressions provided by the
279 <a href="http://www.pcre.org/">PCRE</a> library.</dd>
281 <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
282 an <em>origin server</em>. This is useful to hide the real origin
283 server from the client for security reasons, or to load balance.</dd>
285 <dt><a name="securesocketslayer">Secure Sockets Layer</a> <a name="ssl">(SSL)</a></dt> <dd>A protocol created by Netscape
286 Communications Corporation for general communication authentication
287 and encryption over TCP/IP networks. The most popular usage is
288 <em>HTTPS</em>, i.e. the HyperText Transfer Protocol (HTTP) over SSL.<br />
289 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
291 <dt><a name="serversideincludes">Server Side Includes</a> <a name="ssi">(SSI)</a></dt> <dd>A technique for embedding processing
292 directives inside HTML files.<br /> See: <a href="howto/ssi.html">Introduction to Server Side Includes</a></dd>
294 <dt><a name="session">Session</a></dt>
295 <dd>The context information of a communication in general.</dd>
297 <dt><a name="ssleay">SSLeay</a></dt>
298 <dd>The original SSL/TLS implementation library developed by
301 <dt><a name="symmetriccryptophraphy">Symmetric Cryptography</a></dt>
302 <dd>The study and application of <em>Ciphers</em> that use a single secret key
303 for both encryption and decryption operations.<br />
304 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
306 <dt><a name="tarball">Tarball</a></dt>
307 <dd>A package of files gathered together using the <code>tar</code>
308 utility. Apache distributions are stored in compressed tar archives
311 <dt><a name="transportlayersecurity">Transport Layer Security</a> <a name="tls">(TLS)</a></dt> <dd>The successor protocol to SSL, created
312 by the Internet Engineering Task Force (IETF) for general
313 communication authentication and encryption over TCP/IP networks. TLS
314 version 1 and is nearly identical with SSL version 3.<br />
315 See: <a href="ssl/">SSL/TLS Encryption</a></dd>
317 <dt><a name="uniformresourcelocator">Uniform Resource Locator</a> <a name="url">(URL)</a></dt> <dd>The name/address of a resource on the
318 Internet. This is the common informal term for what is formally
319 called a <a href="#uniformresourceidentifier">Uniform Resource
320 Identifier</a>. URLs are usually made up of a scheme, like
321 <code>http</code> or <code>https</code>, a hostname, and a path. A
323 <code>http://httpd.apache.org/docs-2.1/glossary.html</code>.</dd>
325 <dt><a name="uniformresourceidentifier">Uniform Resource Identifier</a> <a name="URI">(URI)</a></dt> <dd>A compact string of characters for
326 identifying an abstract or physical resource. It is formally defined
327 by <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>.
328 URIs used on the world-wide web are commonly referred to
329 as <a href="#url">URLs</a>.</dd>
331 <dt><a name="virtualhosting">Virtual Hosting</a></dt> <dd>Serving
332 multiple websites using a single instance of Apache. <em>IP virtual
333 hosting</em> differentiates between websites based on their IP
334 address, while <em>name-based virtual hosting</em> uses only the name
335 of the host and can therefore host many sites on the same IP
336 address.<br /> See: <a href="vhosts/">Apache Virtual Host
337 documentation</a></dd>
339 <dt><a name="x.509">X.509</a></dt> <dd>An authentication certificate
340 scheme recommended by the International Telecommunication Union
341 (ITU-T) which is used for SSL/TLS authentication.<br /> See: <a href="ssl/">SSL/TLS Encryption</a></dd>
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