Php may be run as an Apache module. This configuration is known as mod_php. It may also be run as a FPM server or a Fast CGI server.
In the Fast CGI configuration, the Php binary is accessed by the web server using the Fast CGI protocol.
In the Php FPM configuration, the Php is managed by a Fast CGI server called Php FPM. The webserver communicates with this Php FPM server over a TCP socket.