Sentence:  The term <WSD>sweet spot</WSD> is used in describing that point or region of a tennis racket where the ball should be hit for optimum results. There are several definitions of this term, each one based on different physical phenomenon. 
Meaning of the word marked with <WSD> tags:  Any of several places on a bat, racquet, etc., with which to hit a ball, resulting in the latter rebounding with some optimal desirable effect, such as minimum vibration or maximum velocity.