Apache is a web server that add parsers as modules (php). NGINX is a reverse proxy/web server that can proxy to other processes listening on other ports. (PHP-FastCGI running on port 3000).

BROWSER -> NGINX (80) -> PHP-FastCGI (3000) -> NGINX -> BROWSER

NGINX can also proxy on sockets

BROWSER -> NGINX (80) -> PHP-FastCGI (/usr/socks/php.socks) -> NGINX -> BROWSER

CGI just defines the interface, and the language would be implementing the interface.