A shot hit between the legs, usually while running away from the net to chase down a lob. It's a desperation shot turned highlight reel moment. Federer's tweener against Djokovic at the 2009 US Open might be the most famous single shot in tennis history. When it works, the crowd loses its mind. When it doesn't, at least you tried something cool.
"She's chasing down the lob, back to the net, and hits a tweener that lands on the line. The crowd goes absolutely ballistic."