There's COMPACAF, COMPACFLT, COMSCOCENT and literally dozens and dozens of others. In short, when you see these designations, it's a reference to either the senior officer in command or office in charge. In the examples above, we're mentioning the Commander of Pacific Air Forces, the Commander of the Pacific Fleet (seal shown at inset) and the Commander of Special Operations Command, US Central Command.
This designation can be scaled all the way down to a squadron of destroyers (COMDESRON) or on up. The abbreviation is so widely used that the DOD's Dictionary of Military and Associated Terms, our source for these pieces, dedicates three whole pages to its many varieties.
Despite standing for a commander, it should not be confused with the naval rank of commander, which is abbreviated to CMDR, or with COMM, which is short for communications.