While copyrights protect expressions but not ideas, patents cover ideas but not expressions. According to the United States Patent Office:
A patent is an intellectual property right granted by the Government of the United States of America to an inventor “to exclude others from making, using, offering for sale, or selling the invention throughout the United States or importing the invention into the United States” for a limited time in exchange for public disclosure of the invention when the patent is granted.
A slightly more generic definition can be found on the World Intellectual Property Organization (WIPO) website:
A patent is an exclusive right granted for an invention, which is a product or a process that provides a new way ...