underground bank; clandestine bank
Refers to an illegal, unlicensed financial operation that provides banking services outside regulatory oversight, often associated with loan sharks or money laundering.
The police are cracking down on underground banks.
Using an underground bank carries the risk of being forced into high-interest loans.
ヤミ金融 is a broader term for illegal lending operations, while 地下銀行 specifically implies a clandestine banking institution that may handle deposits, transfers, or currency exchange.
銀行 is a legal, licensed bank. 地下銀行 is its illegal counterpart, operating in secret.
Compound of 地下 (underground, clandestine) and 銀行 (bank). The term is a straightforward calque of the English 'underground bank'.