A high, arcing shot aimed over an opponent who's at the net. Offensive lobs have topspin and dip down quickly. Defensive lobs are hit high to buy time when you're out of position. A perfectly placed topspin lob over a net player's head is one of the most humiliating shots in tennis. The overhead smash exists specifically to punish bad lobs.
"She hits a gorgeous topspin lob over his outstretched racquet. It lands on the baseline. He just stands there."