Despite the recognition of the importance of the anatomical extent of venous reflux, its description in medical literature is inconsistent in terms and classifications. Recent international consensus documents provide clear definitions for the three main classes of reflux: segmental, multi-segmental, and axial. This report addresses the most important aspects of the standard definitions of the anatomical extent of venous reflux, the differences between the three classes of reflux, and the challenges of implementing this classification in clinical practice.