Authentication is any process by which you verify that someone is who they claim they are. Authorization is any process by which someone is allowed to be where they want to go, or to have information that they want to have.
Access control refers to the process of restricting, or granting access to a resource based on arbitrary criteria. There are a variety of different ways that this can be accomplished.
See: Access Control
The CGI (Common Gateway Interface) defines a way for a web server to interact with external content-generating programs, which are often referred to as CGI programs or CGI scripts. It is a simple way to put dynamic content on your web site. This document will be an introduction to setting up CGI on your Apache web server, and getting started writing CGI programs.
See: CGI: Dynamic Content
.htaccess files.htaccess files provide a way to make configuration
changes on a per-directory basis. A file, containing one or more
configuration directives, is placed in a particular document directory,
and the directives apply to that directory, and all subdirectories thereof.
See: .htaccess files
SSI (Server Side Includes) are directives that are placed in HTML pages, and evaluated on the server while the pages are being served. They let you add dynamically generated content to an existing HTML page, without having to serve the entire page via a CGI program, or other dynamic technology.
On systems with multiple users, each user can be permitted to have a
web site in their home directory using the http://example.com/~username/ will get content
out of the home directory of the user "username", out of
the subdirectory specified by the