Colloquial and a bit playful — what kids would say. The plain medical/neutral form is 肚脐 (dùqí) without 眼; the suffix 眼 ("hole, eye") makes it more visual and conversational. In Beijing speech you'll often hear it with -儿: 肚脐眼儿 (dùqíyǎnr).
memory
Compound logic: 肚 (belly) + 脐 (navel/umbilicus) + 眼 (hole) — "the hole at the belly's navel." Each piece carries meaning, so the word is fully transparent once you know the parts.
