What does "put up or shut up" mean?

Act on what you are saying or stop talking about it, as in You've been citing evidence for months but never presented it—now put up or shut up. This somewhat impolite term, often put as a command, is believed to come from gambling, in which a card player is told to ante up or withdraw. A second theory maintains that it means either put up your fists to fight or back down. [1870s] Also see put one's money where one's mouth is.