A word, name, symbol, or devise used by a manufacturer to distinguish his goods from those sold by others.

Source: U.S. Courts

Protect words, names, symbols, sounds, or colors that distinguish goods and services from those manufactured or sold by others and to indicate the source of the goods. Trademarks, unlike patents, can be renewed forever as long as they are being used in commerce.

Source: U.S. Patent and Trademark Office.