noun
strutting; sticking out the chest; arched posture
Describes a posture where the body is arched backward, chest thrust out, often with a proud or confident air. Used in contexts like martial arts, dance, or describing someone's bearing.
彼は反り身になって歩いている。
He walks with his chest stuck out.
相撲の稽古で反り身の姿勢を直された。
In sumo practice, my arched-back posture was corrected.
Compound of 反り (そり, 'bend, warp') + 身 (み, 'body'), literally 'bent body'. The exact historical derivation is uncertain, but the meaning is transparent from its components.