Final answer:
Generic equivalent drugs are listed under the 'therapeutic equivalence' category in the FDA's Orange Book, indicating they are interchangeable with their brand-name counterparts.
Step-by-step explanation:
Generic equivalent drugs are listed in the Orange Book under the category of therapeutic equivalence. Specifically, the U.S. Food and Drug Administration (FDA) categorizes these drugs as such to indicate that they are interchangeable with their brand-name counterparts in terms of safety, quality, and efficacy. This categorization is crucial for ensuring that when patents expire, other companies can manufacture and market generic drugs that are just as effective as the original brand-name drugs, fostering competition and making medications more affordable.