Definition:

It is a minimum or sufficient balance , demanded by the bank to maintain the bank account/ investment account.

Explanation:

Basically, this account may be established to assure that a client has necessary/sufficient capital to deal with a trade .On the other hand, a bank may establish a account minimum either to receive fee against opening an account / receive waiver of account services fee or merely to keep the account open . It is free of cost to open a client account furthermore, a financial institution establish such accounts to assure that their systems are not going to be jam with thousand of dormant accounts containing very small amount of money but bank charge some fee against services.