Nolo's Plain-English Law Dictionary
A rule, essentially terminated in 2013, that required a patent application to be filed within one year of: 1) any public use of the invention by the inventor, 2) a sale of the invention, 3) an offer to sell the invention, or 4) any description of the invention by the inventor in a published document. Failure to file a patent application within this one-year period resulted in the invention's passing into the public domain, where it was no longer eligible for a patent. The application of the one-year rule to sales was sometimes referred to as the on-sale bar. With some exceptions, the one-year rules cited above were largely pulled back in 2013 when the U.S. switched to a first-to-file system. After that date, anything published or sold prior to filing of the application will be considered prior art unless it qualifies under a very limited one-year grace period for certain disclosures or sales by the inventor. For the details on this exception, see 35 U.S.C. section 102.