Section 2(f) of the Lanham Act allows a trademark to be registered if it has acquired distinctiveness through secondary meaning, even if it is initially descriptive. This means that a mark, which may not be inherently distinctive, can still gain legal protection if consumers have come to recognize it as identifying the source of a product or service. Understanding this provision is crucial in assessing how descriptive terms can achieve trademark status and how trade dress can also be protected based on distinctiveness.