The discoid meniscus is a morphologic variant associated with altered biomechanics and an increased risk of tearing, yet the systems used to classify it have historically emphasized shape over function. This review examines how classification of the discoid meniscus has evolved, from early morphologic schemes such as the Watanabe classification to more comprehensive frameworks that account for peripheral rim stability, tear characteristics, and functional relevance. We discuss later systems proposed by Klingele, Good, and Yang, which recognized rim stability and tear patterns as key determinants of symptoms and surgical management, and we describe how the PRiSM classification consolidates these advances into a standardized, reproducible system incorporating morphology, thickness, stability, and tear characteristics. We further frame the discoid meniscus as a biomechanical entity in which disorganized collagen, abnormal peripheral attachment, and impaired hoop-stress transmission shape tissue behavior and healing potential. Finally, we argue that future classification systems should integrate morphologic, biomechanical, compositional, and imaging biomarkers to better characterize tissue quality, predict repair outcomes, and guide patient-specific, tissue-preserving treatment. Uniting structure and function within a single framework may improve prognostication and surgical planning.