via:
https://stackoverflow.com/questions/2712825/what-is-mod-phpThere are (at least) two ways of running PHP, when working with Apache :
Using CGI : a PHP process is launched by Apache, and it is that PHP process that interprets PHP code -- not Apache itself
Using PHP as an Apache module (called mod_php) : the PHP interpreter is then kind of "embedded" inside the Apache process : there is no external PHP process -- which means that Apache and PHP can communicate better.