Which of the following definitions best describes a trademark?

A trademark is defined as a symbol, word, or phrase that is legally registered or established by use as representing a company or product. The purpose of a trademark is to identify and distinguish the source of goods or services of one party from those of others. This identity helps consumers recognize and trust the products associated with that trademark, ensuring that they can identify the qualities and characteristics of goods linked to a specific brand.

The other options do not appropriately define a trademark. Protection for a new invention pertains to patents, which grant rights to inventors for their innovative creations. Legal protection for useful ideas is also related to patents or trade secrets rather than trademarks. A method of copyright infringement deals with unauthorized use of copyrighted material, which is separate from the function of trademarks. Thus, the definition that accurately captures the essence of a trademark is the one that focuses on its role in identifying and distinguishing goods in the marketplace.