The tennis shot hit with the back of the hand facing the net is called a backhand.
For a right-handed player, a standard one-handed backhand is usually struck from the left side of the body; for a left-handed player, the sides are reversed. The stroke can also be played with two hands, as used by many modern professionals. In either version, the player’s racket-side hand is positioned so the back of the hand generally faces the opponent at contact.
A backhand is a groundstroke when hit after the ball bounces, but the same side of the racket can be used for backhand volleys, slices and defensive lobs. That is why “backhand” describes the stroke’s side and mechanics, not just one particular speed or trajectory.
The common opposite is the forehand, where the palm-side orientation is generally toward the ball at contact. A slice is a type of backhand or forehand hit with backspin, while a volley describes hitting before the ball bounces; neither term replaces the basic stroke name.