The excerpts for these tags are the same:
FastCGI is a protocol for interfacing interactive programs with a web server. FastCGI is a variation on the earlier Common Gateway Interface (CGI); FastCGI's main aim is to reduce the overhead associated with interfacing the web server and CGI programs, allowing a server to handle more web page requests at once.
There are even some 27 questions with both tags at the same time.
Update: I now have enough rep on Stack Overflow to propose tag synonyms, but I still can't do this on my own because “creating a tag synonym requires 5 score in this tag”.