大腿 literally means 'big leg' and refers specifically to the upper part of the leg—the section between the hip and the knee. While 大 (dà) means 'big' or 'large', and 腿 (tuǐ) means 'leg', together they form a fixed noun that does not imply size comparison but rather denotes the anatomical thigh. This term is used in medical, fitness, and everyday contexts when discussing body parts, injuries, or physical activity.

In daily speech, 大腿 is neutral and widely understood across age groups and regions. It appears frequently in health discussions (e.g., muscle pain, bruising), sports training (e.g., strengthening the thighs), and casual descriptions (e.g., 'my thigh hurts'). Unlike English, Chinese rarely uses modifiers like 'upper leg'—大腿 is the standard, unambiguous term for this body region. It is never used metaphorically in formal contexts, though colloquially it can appear in idioms like 抱大腿 (bào dà tuǐ, 'to cling to a powerful person'), which is informal and figurative.