Estoppel is a legal term of art for "stopping" certain outcomes requested by a party to a lawsuit. In trademark litigation, the plaintiff is said to be estopped from claiming infringement if plaintiff's actions, or lack thereof, indicated approval of defendant's use of the trademark (acquiescence). Also, Estoppel applies to stop the plaintiff from claiming trademark infringement where the plaintiff delayed for an unreasonably long period of time before beginning enforcement against defendant (laches).