Renin is primarily classified as an enzyme that plays a crucial role in the body's renin-angiotensin system, which regulates blood pressure and fluid balance. It is secreted by the kidneys and acts on angiotensinogen to produce angiotensin I, leading to further hormonal activity. While it has hormone-like effects, its primary function is enzymatic. The confusion arises from its dual role in the physiological processes. Ultimately, renin is best understood as an enzyme with significant hormonal implications.