PHP, or PHP Hypertext Preprocessor (a recursive initialism) is one of the most popular server-side languages on the web. Most popular CMSs are written PHP, as well as thousands of custom web sites. Originally based on C with influence from Perl/CGI scripting, PHP has matured into a powerful procedural and object-oriented language.
PHP is an interpreted language, meaning that scripts (or programs) written in PHP are interpreted at run time. This is in contrast to compiled languages, where the original source code would be compiled into a binary file which is then executed on the target system. There are pros and cons to each method. The primary advantage of interpreted languages is the ability to make instantaneous changes to the source code and see the results without undergoing extra compilation steps. The primary advantage of compiled code is the ability to run the generated executable file on a compatible system without the need for extra programs or libraries, and the inability or difficulty for end-users or competitors to decompile the binary back to usable source code.