松弛 (sōng chí) is an adjective meaning 'slack', 'loose', or 'relaxed', especially describing a physical state where tension, tightness, or rigidity has decreased. The character 松 (sōng) means 'loose', 'relaxed', or 'unfastened', while 弛 (chí) means 'to relax', 'to slacken', or 'to ease'. Together, they form a compound emphasizing the release of physical tension—commonly used for muscles, skin, ligaments, or mechanical parts. It often appears in medical, fitness, and wellness contexts, such as describing muscle relaxation after exercise or age-related loss of skin elasticity.

Unlike general terms like 放松 (fàngsōng), which refers to mental or intentional relaxation, 松弛 focuses on a passive, observable physical condition—often neutral or slightly negative when implying weakness or decline (e.g., 'sagging' skin or 'loose' joints). It rarely describes emotions or abstract states, and is not used for people’s demeanor in social situations (use 轻松 or 自然 instead).