[Reiwa]

Equitable estoppel

This common-law doctrine prevents a party from asserting a claim if their previous conduct or statements led another party to believe a certain outcome, and that party relied on it to their detriment.
In patent law, it may prevent a patent owner from enforcing their patent against an infringer if they previously misled the infringer into believing they would not enforce their rights.

In trademark law, equitable estoppel (also called acquiescence) can be a defense to infringement. It applies if the trademark owner's past conduct or inaction indicated approval of the defendant's use of the mark, and the defendant relied on that apparent approval.