臂膊 (bì bó) is a literary or classical term for 'arm', referring to the entire upper limb from shoulder to wrist. Though composed of two characters—臂 (bì), meaning 'arm' or 'upper limb', and 膊 (bó), meaning 'shoulder' or 'upper arm'—together they form a compound that emphasizes the arm as a strong, functional part of the body, often evoking physical strength, labor, or traditional imagery. It appears frequently in classical texts, idioms, martial arts descriptions, and formal or poetic contexts, but is rarely used in everyday spoken Mandarin.

In modern spoken Chinese, people almost always say 手臂 (shǒu bì) or simply 手 (shǒu, though this usually means 'hand') in casual contexts. 臂膊 carries a slightly archaic, vivid, or emphatic tone—often highlighting muscularity, exertion, or bodily presence. You’ll encounter it in literature describing warriors, farmers, or laborers, or in fixed expressions like 振臂膊 (zhèn bì bó, 'to raise one’s arm'—figuratively, to rally others).