腹 is the literary/formal word for belly. In everyday speech, 肚子 (dùzi) is used instead. 腹 appears in many compounds: 腹部 (abdomen), 空腹 (empty stomach), 腹泻 (diarrhea), 满腹 (full of, figurative).
memory
The radical 月 (meat/body part) on the left tells you it's a body part. 复 (fù) on the right gives the pronunciation.
