A shot hit with backspin (underspin), where the racquet moves from high to low through the ball. The ball stays low after bouncing, skidding through the court. Used defensively to buy time, offensively to change pace, and on approach shots to keep the ball low. Federer's backhand slice was a thing of beauty. Most players use slice as a tactical weapon rather than a primary groundstroke.
"Low, skidding slice backhand that stays ankle-height after the bounce. Good luck doing anything aggressive with that return."