In patent law, anticipation refers to the prior invention or disclosure of the claimed invention by another, or the inventor's own disclosure of the claimed invention by publication, sale, or offer to sell prior to the inventor's application for a patent. In other words, if someone else has known about or used the invention before the patent applicant applies for a patent, that patent applicant will not be entitled to a patent.
Anticipation is a grounds for invalidating or rejecting a patent because it means that the claimed invention lacks novelty. Patent invalidity based on lack of novelty, or anticipation, requires that the invention was known or used by others before it was invented by the patentee.
Messerschmidt v. U.S., 29 Fed. Cl. 1 (1993)
Hoover Group, Inc. v. Custom Metalcraft, Inc., 66 F.3d 299 (Fed. Cir. 1995)