noun
dormant account; inactive bank account
A bank account with no deposits or withdrawals for a long period, where the depositor's rights may have lapsed under banking regulations.
長期間使っていない口座は睡眠預金になることがある。
An account that hasn't been used for a long time may become a dormant account.
休眠口座 is a more common term for a dormant account, while 睡眠預金 is a specific legal/financial term emphasizing the deposit itself and the lapse of rights.
Compound of 睡眠 (sleep) and 預金 (deposit), literally 'sleeping deposit'. The term describes a deposit that is metaphorically 'asleep' due to inactivity.