A shot hit above your head, similar to a serve motion, typically used to put away a weak lob. Also called a smash. This should be a free point, which is why missing an overhead is one of the most embarrassing things that can happen on a tennis court. The ball is up there, you have time, and you still hit it into the net? Rough.
"Easy overhead at the net. He winds up, smashes it into the open court. Point over."