I sometimes hear beginners or noobs calling an M4 or an AK47 a "machine gun". I then tell them it's not a machine gun, and it's an assault rifle. I was on Yahoo Answers answering some airsoft question, and I said how the M249 was a type of machine gun, whereas the M4 is an assault rifle, and not called a machine gun necessarily. Then someone said this: "LOL the guy below me is a ******. the first one is a LIGHT MACHINE GUN (The m249) while the M4 he listed is a Assult rifle (still a machine gun). Again, they are both machine guns just different types." So what is a machine gun?