Apache is The WebServer for Linux and one of the critical components of LAMP.

Well, actually, it is now the umbrella name for a whole range of OpenSource projects under the reign of the ApacheSoftwareFoundation. The WebServer is but one of many their projects. In their own words

The Apache HTTP Server Project is an effort to develop and maintain an OpenSource HTTP server for modern OperatingSystems including UNIX and WindowsNT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.

Apache has been the most popular WebServer on the InterNet since April of 1996. The July 2003 Netcraft WebServer Survey found that 63% of the WebSites on the InterNet are using Apache, thus making it more widely used than all other WebServers combined.

It runs on most OpenSource (and not so open source) OperatingSystems. It started life as a heap of patches for NCSA's at the time no longer maintained httpd, circulating among SysAdmins. Eventually, a group of developers collected all the patches and consolidated them into their own version of the web server. Hence the name, a play on words on “A Patchy Server.”

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