noun
side of the body; flank
Refers to the lateral part of the torso, from armpit to hip. Common in medical, fitness, and anatomical contexts.
体側を伸ばすストレッチを毎日行っている。
I do a stretch that extends the side of my body every day.
医者は患者の体側に発疹を確認した。
The doctor found a rash on the patient's flank.
脇腹 is a more common, everyday word for the side of the abdomen or flank, while 体側 is more technical and often used in medical or fitness contexts.
Compound of 体 (body) and 側 (side). The reading is on'yomi for both characters.