Trademark distinctiveness is an important concept in the law governing trademarks and service marks. A trademark may be eligible for registration, or registrable, if it performs the essential trademark function, and has distinctive character. Registrability can be understood as a continuum, with "inherently distinctive" marks at one end, "generic" and "descriptive" marks with no distinctive character at the other end, and "suggestive" and "arbitrary" marks lying between these two points. "Descriptive" marks must acquire distinctiveness through secondary meaning—consumers have come to recognize the mark as a source indicator—to be protectable. "Generic" terms are used to refer to the product or service itself and cannot be used as trademarks.