Over-trumping means that when a trump has already been played to a trick and you also play a trump, you must play a higher trump than the one before it if you can. This obligation, often called playing over the trump, applies when you are void in the led suit and choose to trump. If you hold a trump higher than the highest one already in the trick, you are required to beat it rather than throw a low trump. If you cannot beat it, you may play a lower trump or discard. This rule keeps trumps competitive and stops players from dumping weak trumps cheaply.