PHP is a server-side scripting language designed for web development but also used as a general-purpose programming language.
Originally created by Rasmus Lerdorf in 1994, the PHP reference implementation is now produced by The PHP Group.
It originally stood for Personal Home Page, but it now stands for the recursive acronym : Hypertext Preprocessor
It may be embedded into HTML code, or it can be used in combination with various web template systems, web content management systems, and web frameworks.
As you should know it is usually processed by a interpreter implemented as a module in the web server or as a Common Gateway Interface (CGI) executable.
The web server combines the results of the interpreted and executed code, which may be any type of data, including images, with the generated web page.
It may also be executed with a command-line interface (CLI) and can be used to implement standalone graphical applications.