A baseball term.
A check-swing is when a batter starts to swing at a ball, but stops the swing just before the ball reaches home plate. It's the first or third base umpire's job to decide whether it's a real check-swing (in which case a ball may be called) or a strike (swung at and missed).
If a check-swing hits the ball, it's played as normal. A check-swing does count as an at-bat, and is therefore calculated in your batting average. (A bunt may not be).