Sentence:  Most of us are familiar with the existence of a ‘<WSD>sweet spot</WSD>' on a tennis racket or bat: the place where it is best to strike the ball. ... Physicists call this <WSD>sweet spot</WSD> the ‘centre of percussion' and it occurs at a distance from the top of a cricket or baseball bat that is about two thirds of its total length. 
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.