An FCGI file is a source code file that contains source code written for FastCGI (FCGI). It can be written in several different programming languages and contains the extension of CGI standard used for more robust handling of Web server requests. The most commonly support languages for FCGI includes Perl that provides support for both Perl code and the strong external interface of FastCGI API.
FCGI File Format
What makes an FCGI file important? FCGI interface supports distributed computing to handle web requests and distribute them across multiple servers. This makes FCGI files mostly used for load balancing across multiple servers.