Ken Larsen's Backgammon - TEMPO tactic
Tempo Hit. You hit just to take away part of your opponent's next roll, so he can't use the entire roll to harm you on his side of the board or create a formidable position like multiple anchors. Tempo hits are most successful when your opponent has a very weak home board.
In the position shown, Bar/18 would be a 0.052 error.