Butterfly stroke (dié yǒng) is one of the four competitive swimming strokes, characterized by simultaneous overhead arm movements and a dolphin-like undulating kick. The name literally combines 蝶 (dié), meaning 'butterfly', and 泳 (yǒng), meaning 'to swim'. This vivid metaphor reflects the stroke’s graceful, wing-like arm motion — reminiscent of a butterfly’s flight — rather than any biological connection to the insect itself.

The term is used exclusively in sports and physical education contexts, especially in competitive swimming, coaching, or fitness instruction. It’s a formal, technical term — not used colloquially to describe casual swimming. Learners should note that while 蝶 means 'butterfly', the word 蝶泳 never refers to actual butterflies or their behavior; it is a fixed compound noun with no separable meaning in everyday speech.