Short for
football. Refers to games that involve
kicking a football at some point, although some of these
team sports involve more throwing of and running with the
football.
Depending on which part of the world you are in it can mean many different games. These games may have other names that are specific to their rules, for example most people in the United Kingdom refer to soccer when they mention footy, whereas in Australia, footy refers to Australian Rules or Rugby League, depending on which state you're from.
thanks Proguar for the reminder about the North Eastern states preferred code.
In the United Kingdom, a lot of people think it is wrong to call Australian Rules footy because people hold the ball with their hands, although it should be noted that the skill of kicking an oval ball is central to the game and, interestingly enough the term for kicking the ball off the ground without touching it with ones hands is soccering.
Confused?
Good. Footy's one of those things you wont understand by reading about them.