Categories: Common language, Familiar
🇫🇷 (une, la) poche [NF], connaître/connaitre* (qqc, un lieu) comme sa poche [EXPR]
Nota bene: * connaitre (without circumflex accent) is also valid since 1990 spelling rectifications of French orthography. [Link]
Synonyms or related terms: poche marsupiale