The female equivalent of the cock block, but amongst two girls who'd like to get it on. A much more graphic term to use than box lock.
Trent is hanging out with a bunch of his lesbian friends at a bar. One of his friends' name is Lily.
Lily: That girl at the bar is so hot. I'm going to go hit on her.
Trent: No, I'm cranky. Let's go home.
Lily: Ok fine.
Trent has just clam jammed Lily.
Prices shown in USD.