Section 2(f) claims refer to a provision in the Lanham Act that allows a trademark applicant to establish that a mark has acquired distinctiveness through use in commerce, even if the mark is initially considered descriptive. This means that the applicant can argue that consumers have come to associate the mark with their goods or services due to its use over time, thus qualifying it for protection. This concept ties into acquired distinctiveness and secondary meaning as it focuses on how consumer perception can change based on experience and marketing efforts.