What does "slam dunk" mean?

A forceful, dramatic move, as in That indictment was a slam dunk if ever there was one. This expression is also often put as a verb, slam-dunk, meaning “make a forceful move against someone,” as in This is a great chance for us to slam-dunk the opposition. The idiom comes from basketball, where it refers to a dramatic shot in which the ball is thrust into the basket from above the rim. It was transferred to other activities from about 1980 on.