PHP is an HTML-embedded scripting language.
PHP attempts to make it easy for developers to write dynamically generated webpages.
PHP also offers built-in database integration for several commercial and non-commercial database management systems, so writing a database-enabled webpage with PHP is fairly simple.
The most common use of PHP coding is probably as a replacement for CGI scripts. The mod_php package contains the module which adds support for the PHP language to Apache HTTP Server V2.4.X.