A more thorough explanation:

Definition: The on-sale bar is a legal rule that prevents an invention from being patented if it was sold or offered for sale more than one year before the patent application is filed. This rule is outlined in 35 USCA § 102(b).

Example: Let's say that John invents a new type of bicycle chain and starts selling it to bike shops in January 2020. If John waits until January 2021 to file a patent application for his invention, he may be barred from obtaining a patent because the invention was already on sale for more than a year.

Explanation: The on-sale bar is designed to prevent inventors from delaying the filing of a patent application while they try to profit from their invention. If an inventor waits too long to file a patent application, they may lose the ability to obtain a patent altogether. In the example above, John would have had to file his patent application before January 2021 in order to avoid the on-sale bar.