A more thorough explanation:

A Walker Process claim is a type of counterclaim that can be made in an infringement lawsuit. It seeks a declaratory judgment that the patent in question is invalid because the owner of the patent defrauded the Patent Office. This claim is based on antitrust law and alleges that the patent owner wrongfully tried to monopolize a market.

For example, if a company sues another company for patent infringement, the defendant may file a Walker Process claim as a defense. They would argue that the patent is invalid because the owner obtained it through fraudulent means and is using it to unfairly dominate the market.

The term "Walker Process" comes from a landmark Supreme Court case, Walker Process Equip., Inc. v. Food Mach. & Chem., which established the legal basis for this type of claim.