Legal estoppel is estoppel resulting from a statement in deed or official record. According to U.S. patent law, a grantor is prohibited from denying the validity of title to a subject matter that has been assigned. Legal estoppel originally evolved from estoppel by deed and the Supreme Court extended legal estoppel to patents in Westinghouse Electric & Mfg. Co. v. Formica Insulation Co., 266 U.S. 342 (U.S. 1924). A statement from the case’s holding would help add meat to this defn.
The following is an example of a case law defining legal estoppel:
Legal estoppel refers to a narrow category of conduct encompassing scenarios where a patentee has licensed or assigned a right, received consideration, and then sought to derogate from the right granted.[TransCore, LP v. Elec. Transaction Consultants Corp., 563 F.3d 1271 (Fed. Cir. 2009)]