This refers to the balls and strikes that the umpire is calling on the batter. For example the count might be 1 and 2, which just means that 1 ball and 2 strikes have been called against the batter. Just remember that when you hear an announcer say the count is 2 and 1 that balls are first and strikes are last. So that is 2 balls and 1 strike. A full count is 3 and 2, meaning that the next pitch will either be a ball and the batter will get a walk or it will be a strike and the batter will be out. Of course there could be a lot of foul balls before either one of these things happen or the batter could get a hit.