手臂(shǒu bì) - arm in Mandarin

手臂 (shǒu bì) is the arm, from shoulder to wrist. It is the neutral, slightly formal word you will meet in writing, in medical contexts and in careful speech, and it is the one worth learning first because it is unambiguous.

Everyday northern speech more often says 胳膊 (gēbo) for the same body part, and 手 on its own frequently stretches to cover the whole arm in casual sentences. So 抬起手 and 举起手臂 can describe the same movement, with the second sounding more deliberate.

The trap runs the other way from what English speakers expect. In English hand and arm are strictly separate; in Chinese 手 is elastic and will happily swallow the arm, while 手臂 stays precise. If you need to be clear about which part you mean, use 手臂, and note that 臂 never appears alone as a word.