The Apache HTTP Server, commonly called Apache, is web server software notable for playing a vital role in the initial growth of the World Wide Web. In 2009, it became the first web server software to surpass the 100 million website milestone. Apache was the first viable alternative to the Netscape Communications Corporation web server and since has evolved to dominate other web servers in terms of functionality and performance. Typically, Apache is run on a Unix-like operating system.

The Apache web server, more popular than simply, represents an open-source web server platform based on most of the websites we see today on the World Wide Web. Looking back at when it was introduced in the ’90s and gradually adopted as a preferred server platform on the web, we could state that Apache acted as the main driving force behind today’s web expansion. As a web server ‘pioneer’, Apache has become a standard for developing other successful web server platforms.

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The application is available for various operating systems, including Unix, FreeBSD, Linux, Solaris, Novell NetWare, Mac OS X, and Microsoft Windows. Released under the Apache License, Apache is open-source software.

Since April 1996, Apache has been the most popular HTTP server software. As of March 2012, Apache was estimated to serve 57.46% of all active websites and 65.24% of the top servers across all domains.

According to the Apache project website FAQ, the name Apache was chosen out of respect to the Native American tribe Apache and its superior skills in warfare and strategy. The website also explains the widespread but erroneous origin of the name, A Patchy Server (since it was a conjunction of software patches).

Apache provides a variety of Multiprocessing Modules (MPMs), which allow Apache to run in a process-based, hybrid (process and thread) or event-hybrid mode to better match the demands of each particular infrastructure. This implies that choosing the correct MPM and the correct configuration is essential. Where compromises in performance need to be made, the design of Apache is to reduce latency and increase throughput relative to simply handling more requests, thus ensuring consistent and reliable processing of requests within reasonable time frames.

Some of the capabilities supported by the server include support for CGI (Common Gateway Interface) and SSI (Server Side Includes), URL redirection, automatic directory listings, user authentication, anonymous user accessibly, loading modules support, HTTP header metafiles, proxy caching abilities, etc.

These are the reasons why an Apache server is used for web hosting, and this is called Apache web hosting.