Literally 'three strokes, two strokes' — picture someone making just 3-2 quick motions to finish a task. The doubled 下 (a measure word for actions/strokes) creates the sense of brisk, minimal effort.
register
Colloquial and lively; common in spoken Chinese and casual writing. Pairs naturally with 就 (jiù, 'and then immediately') as in 三下两下就… ('and just like that…').
