"Prosecution History Estoppel" is a legal doctrine that means a claim is barred because the claimant's prior actions or statements are inconsistent with that claim. That is to say, prosecution history estoppel prevents a patent owner from contradicting the prosecution history by claiming as an equivalent subject matter that was given up during prosecution in order to obtain the patent.
"When...the patentee originally claimed the subject matter alleged to infringe but then narrowed the claim in response to a rejection, he may not argue that the surrendered territory comprised unforeseen subject matter that should be deemed equivalent to the literal claims of the issued patent." Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535, U.S. 722, 733-34 (2002).
"When...the patentee originally claimed the subject matter alleged to infringe but then narrowed the claim in response to a rejection, he may not argue that the surrendered territory comprised unforeseen subject matter that should be deemed equivalent to the literal claims of the issued patent." Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535, U.S. 722, 733-34 (2002).