What is Apache server?
Broadly, Apache refers to the Apache Software Foundation, which is a foundation that supports open source development through a variety of projects. Their most popular project is the Apache HTTP (Hyper Text Transport Protocol) server, which we will hereafter refer to as simply the Apache server. This project started in 1995, and since April 1996 it has been the most popular HTTP server in use.
An HTTP server such as Apache server is a computer program that takes files or programs, and makes them accessible to users through HTTP. The user could be remote across the Internet or intranet, or sitting at the same computer that is running the Apache server. These files could be plain HTML which is transmitted directly to be rendered by the user's browser, or server side programming such as Perl, PHP or Python which dynamically generates HTML to be rendered by the user's browser.
The Apache server differs from its main competitor, Microsoft IIS (Internet Information Server), in that Apache is open source. This means that it can be used without paying licensing fees, and that the source code is freely available for users to view and modify. Apache also runs on a wide variety of hardware and operating system platforms, from Unix and Unix variants, to Microsoft Windows, to MacOS. By far the most common deployment is to run Apache server on Linux, which is the foundation of the increasingly popular LAMP platform (Linux, Apache, MySQL, PHP).