Apache HTTP Server, commonly referred to as Apache, is an open-source web server software solution distributed under the Apache License. Initially deriving from the second-ever web server, NCSA HTTPd developed in 1993, Apache's codebase began as an evolution of NCSA 1.3 but was comprehensively rewritten by the Apache Software Foundation following its establishment in 1999. No original NCSA HTTPd code remains in current Apache releases. As of December 2015, the latest stable version was Apache 2.4.18.
Historically, Apache has been among the most dominant web server platforms globally, achieving a peak market share around 70% in 2005. As of early 2016, Apache held approximately 33% of total websites but remained close to 50% when measuring only active sites—demonstrating its continued prominence across production deployments worldwide.
Apache's modular architecture contributes to its robust security and proven long-term reliability, allowing administrators to extend core capabilities via add-on modules. Furthermore, Apache supports the Common Gateway Interface (CGI), facilitating dynamic web application functionality through integration with external scripts and programming frameworks.
Widely deployed in web application scenarios, Apache frequently forms the cornerstone of "LAMP stack" architectures—Linux OS, Apache web server, MySQL database, and PHP/Perl/Python scripting languages. This stack continues to deliver dependable, scalable, open-source infrastructure across countless global web-based services.