Definitions

Authentication

The positive identification of a network entity such as a server, a client, or a user.
See: Authentication, Authorization, and Access Control

Access Control

The restriction of access to network realms. In an Apache context usually the restriction of access to certain URLs.
See: Authentication, Authorization, and Access Control

APache eXtension Tool (apxs)

A perl script that aids in compiling module sources into Dynamic Shared Objects (DSOs) and helps install them in the Apache Web server.
See: Manual Page: apxs

Certificate

A data record used for authenticating network entities such as a server or a client. A certificate contains X.509 information pieces about its owner (called the subject) and the signing Certificate Authority (called the issuer), plus the owner's public key and the signature made by the CA. Network entities verify these signatures using CA certificates.
See: SSL/TLS Encryption

Certification Authority (CA)

A trusted third party whose purpose is to sign certificates for network entities it has authenticated using secure means. Other network entities can check the signature to verify that a CA has authenticated the bearer of a certificate.
See: SSL/TLS Encryption

Certificate Signing Request (CSR)

An unsigned certificate for submission to a Certification Authority, which signs it with the Private Key of their CA Certificate. Once the CSR is signed, it becomes a real certificate.
See: SSL/TLS Encryption

Cipher

An algorithm or system for data encryption. Examples are DES, IDEA, RC4, etc.
See: SSL/TLS Encryption

Ciphertext

The result after Plaintext is passed through a Cipher.
See: SSL/TLS Encryption

Common Gateway Interface (CGI)

A standard definition for an interface between a web server and an external program that allows the external program to service requests. The interface was originally defined by NCSA but there is also an RFC project.
See: Dynamic Content with CGI

Configuration Directive

See: Directive

Configuration File

A text file containing Directives that control the configuration of Apache.
See: Configuration Files

CONNECT

An HTTP method for proxying raw data channels over HTTP. It can be used to encapsulate other protocols, such as the SSL protocol.

Context

An area in the configuration files where certain types of directives are allowed.
See: Terms Used to Describe Apache Directives

Digital Signature

An encrypted text block that validates a certificate or other file. A Certification Authority creates a signature by generating a hash of the Public Key embedded in a Certificate, then encrypting the hash with its own Private Key. Only the CA's public key can decrypt the signature, verifying that the CA has authenticated the network entity that owns the Certificate.
See: SSL/TLS Encryption

Directive

A configuration command that controls one or more aspects of Apache's behavior. Directives are placed in the Configuration File
See: Directive Index

Dynamic Shared Object (DSO)

Modules compiled seperately from the Apache httpd binary that can be loaded on-demand.
See: Dynamic Shared Object Support

Environment Variable (env-variable)

Named variables managed by the operating system shell and used to store information and communicate between programs. Apache also contains internal variables that are referred to as environment variables, but are stored in internal Apache structures, rather than in the shell environment.
See: Environment Variables in Apache

Export-Crippled

Diminished in cryptographic strength (and security) in order to comply with the United States' Export Administration Regulations (EAR). Export-crippled cryptographic software is limited to a small key size, resulting in Ciphertext which usually can be decrypted by brute force.
See: SSL/TLS Encryption

Filter

A process that is applied to data that is sent or received by the server. Input filters process data sent by the client to the server, while output filters process documents on the server before they are sent to the client. For examle, the INCLUDES output filter processes documents for Server Side Includes.
See: Filters

Fully-Qualified Domain-Name (FQDN)

The unique name of a network entity, consisting of a hostname and a domain name that can resolve to an IP address. For example, www is a hostname, whatever.com is a domain name, and www.whatever.com is a fully-qualified domain name.

Handler

An internal Apache representation of the action to be performed when a file is called. Generally, files have implicit handlers, based on the file type. Normally, all files are simply served by the server, but certain file types are "handled" separately. For example, the cgi-script handler designates files to be processed as CGIs.
See: Apache's Handler Use

Header

The part of the HTTP request and response that is sent before the actual content, and that contains meta-information describing the content.

.htaccess

A configuration file that is placed inside the web tree and applies configuration directives to the directory where it is placed and all sub-directories. Despite its name, this file can hold almost any type of directive, not just access-control directives.
See: Configuration Files

httpd.conf

The main Apache configuration file. The default location is /usr/local/apache2/conf/httpd.conf, but it may be moved using run-time or compile-time configuration.
See: Configuration Files

HyperText Transfer Protocol (HTTP)

The standard transmission protocol used on the World Wide Web. Apache implements version 1.1 of the protocol, refered to as HTTP/1.1 and defined by RFC 2616.

HTTPS

The HyperText Transport Protocol (Secure), the standard encrypted communication mechanism on the World Wide Web. This is actually just HTTP over SSL.
See: SSL/TLS Encryption

Method

In the context of HTTP, an action to perform on a resource, specified on the request line by the client. Some of the methods available in HTTP are GET, POST, and PUT.

Message Digest

A hash of a message, which can be used to verify that the contents of the message have not been altered in transit.
See: SSL/TLS Encryption

MIME-type

A way to describe the kind of document being transmitted. Its name comes from that fact that its format is borrowed from the Multipurpose Internet Mail Extensions. It consists of a major type and a minor type, separated by a slash. Some examples are text/html, image/gif, and application/octet-stream. In HTTP, the MIME-type is transmitted in the Content-Type header.
See: mod_mime

Module

An independent part of a program. Much of Apache's functionality is contained in modules that you can choose to include or exclude. Modules that are compiled into the the Apache httpd binary are called static modules, while modules that are stored seperately and can be optionally loaded at run-time are called dynamic modules or DSOs. Modules that are included by default are called base modules. Many modules are available for Apache that are not distributed as part of the Apache HTTP Server tarball. These are referred to as third-party modules.
See: Module Index

OpenSSL

The Open Source toolkit for SSL/TLS
see http://www.openssl.org/

Pass Phrase

The word or phrase that protects private key files. It prevents unauthorized users from encrypting them. Usually it's just the secret encryption/decryption key used for Ciphers.
See: SSL/TLS Encryption

Plaintext

The unencrypted text.

Private Key

The secret key in a Public Key Cryptography system, used to decrypt incoming messages and sign outgoing ones.
See: SSL/TLS Encryption

Proxy

An intermediate server that sits between the client and the origin server. It accepts requests from clients, transmits those requests on to the origin server, and then returns the response from the origin server to the client. If several clients request the same content, the proxy can deliver that content from its cache, rather than requesting it from the origin server each time, thereby reducing response time.
See: mod_proxy

Public Key

The publically available key in a Public Key Cryptography system, used to encrypt messages bound for its owner and to decrypt signatures made by its owner.
See: SSL/TLS Encryption

Public Key Cryptography

The study and application of asymmetric encryption systems, which use one key for encryption and another for decryption. A corresponding pair of such keys constitutes a key pair. Also called Asymmetric Crypography.
See: SSL/TLS Encryption

Regular Expression (Regex)

A way of describing a pattern in text - for example, "all the words that begin with the letter A" or "every 10-digit phone number" or even "Every sentence with two commas in it, and no capital letter Q". Regular expressions are useful in Apache because they let you apply certain attributes against collections of files or resources in very flexible ways - for example, all .gif and .jpg files under any "images" directory could be written as "/images/.*(jpg|gif)$". Apache uses Perl Compatible Regular Expressions provided by the PCRE library.

Reverse ProxHTTP/1.1 200 OK Date: Mon, 07 Jul 2025 05:16:42 GMT Server: Apache/2.0.42 (Win32) PHP/5.2.10 Content-Location: glossary.html.en Vary: negotiate TCN: choice Accept-Ranges: bytes Content-Length: 19201 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html; charset=ISO-8859-1 Content-Language: en

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Apache HTTP Server Version 2.0

Apache > HTTP Server > Documentation > Version 2.0

Glossary

This glossary defines some of the common terminology related to Apache in particular, and web serving in general. More information on each concept is provided in the links.

Definitions

Authentication

The positive identification of a network entity such as a server, a client, or a user.
See: Authentication, Authorization, and Access Control

Access Control

The restriction of access to network realms. In an Apache context usually the restriction of access to certain URLs.
See: Authentication, Authorization, and Access Control

APache eXtension Tool (apxs)

A perl script that aids in compiling module sources into Dynamic Shared Objects (DSOs) and helps install them in the Apache Web server.
See: Manual Page: apxs

Certificate

A data record used for authenticating network entities such as a server or a client. A certificate contains X.509 information pieces about its owner (called the subject) and the signing Certificate Authority (called the issuer), plus the owner's public key and the signature made by the CA. Network entities verify these signatures using CA certificates.
See: SSL/TLS Encryption