Refers to disclosures and publications in the field of the invention that predate the filing date of the patent in first-to-file countries and for patents filed before the effective date of the America Invents Act, the date of invention in the United States. Prior art is not necessarily invalidating, though the term is often loosely used to refer to invalidating references; it can be and usually is simply technical background. The question of what is prior art is closely tied to the priority date for a patent application.