FastCGI is a web-server plugin program which allows one process to handle multiple CGI(Common gateway interface) requests at once with faster speed.

CGI is a protocol for interfacing external applications to web servers. CGI applications run in separate processes, which are created at the start of each request and torn down at the end.
Instead of creating a new process for each request, FastCGI uses persistent processes to handle a series of requests. Each individual FastCGI process can handle many requests over its lifetime, thereby avoiding the overhead of per-request process creation and termination.