PHP (the acronym is "recursive" and refers back to itself--it stands for PHP: Hypertext Preprocessor) is a popular server-side scripting language. The fact that it is "server-side" means that special software on the web server is used each time a page with PHP is processed. This software responds to specific commands included within (embedded) in the webpage. Generally, these commands tell it to generate new HTML code which is sent back to the user's web browser. Thus, especially when it is connected to a database on a web server, PHP can be used to generate dynamic web content. There are other uses for PHP that do not involve the internet, but this use of PHP is the most common one today. (Coggeshall)

Like some other technologies, PHP is not tied to a specific software vendor, meaning it is relatively compatible with other technologies and databases. This, and the fact that PHP requires relatively simple software to write and run, makes it a popular choice among programmers, who are seeking something more interactive and dynamic than JavaScript, but not as complex or tied to a single company as ASP.NET. Though there is no formal technical specification for PHP, it is maintained de facto by The PHP Group. (PHP: Introduction)

Examples: Like ASP.NET, PHP is broadly used, especially by small and moderately sized websites. Indeed, the original meaning of PHP was Personal Home Page tools, as it was originally built for the maintenance of the personal website of its creator, Rasmus Lerdorf. PHP is also particularly prevalent in online web discussion boards. All PHP pages end in .php rather than .html or .aspx.