What does ab stand for in baseball?

At-bats. The number of batters he faced, not counting those he walked and (I think) those who reached on an error and (maybe) those who "sacrificed" a runner to the next base. I'm not 100% sure which batters are excluded, but I know walks are excluded. Excluded from ABs are walks, sacrifices, sacrifice flies, catcher's interference, and hit by pitch. Reaching base by an error is considered an AB.