35 U.S.C. 102(b): A person shall be entitled to a patent unless – (b) the invention was… on sale in this country, more than one year prior to the date of the application for patent in the United States. In other words, if you have sold, or offered to sell your invention, you have one year to file a patent application for the invention. Failure to do so will cause you to permanently lose your rights to protect your invention. It is also important to know that while the U.S. patent laws provide you a one year grace period, a sale or offer to sell your invention may immediately prevent you from protecting your invention in any other country. The on-sale bar is merely one of the bars to patentability in the US. You can find more information about patentability and bars to patentability in my FAQ answer linked below.