A web server is computer software that delivers web pages on request to clients using the Hypertext Transfer Protocol (HTTP). It serves the files that form web pages to web users; the content is in the form of HTML documents, images, style sheets, and scripts.
Apache is the most popular web server software, implementing the latest protocols, with an excellent feature set, and it is highly configurable and extensible. Apache is used by more than half of all active websites.
However, Apache is not the only capable open source web server. There are many alternative web servers that offer high-performance, but place less demands on hardware. Web servers that use less resources, low memory footprint, and low CPU load are attractive, enabling inexpensive hardware, such as the Raspberry Pi, to be used as a web server.