A phrase that often appears on manufactured items. It means that someone has applied for a patent on an invention that is contained in the manufactured item. It serves as a warning that a patent may issue that would cover the item and that copiers should be careful because they might infringe if the patent issues. Once the patent issues, the patent owner will stop using the phrase "patent pending" and start using a phrase such as "covered by U.S. Patent Number XXXXXXX." Applying the patent pending phrase to an item when no patent application has been made can result in a fine.
Source: U.S. Patent and Trademark Office.