A more thorough explanation:

Definition: The length of time that a patent is valid and enforceable.

Examples:

• Utility patents have a patent term of 20 years from the date of filing.
• Design patents have a patent term of 15 years from the date of grant.

The examples illustrate that the patent term varies depending on the type of patent. Utility patents, which cover new and useful processes, machines, and compositions of matter, have a longer patent term of 20 years. Design patents, which cover new, original, and ornamental designs for an article of manufacture, have a shorter patent term of 15 years. Once the patent term expires, the invention becomes part of the public domain and can be used by anyone without permission or payment to the patent holder.