Special savings account that pays a varying interest rate higher on average than an ordinary savings account’s interest rate. There are constraints on this special account., however. A specific minimum credit balance is required to retain the special interest rate. A limited number of checks can be written on the account in any one month. No limit on fund transfers over the bank’s counter or through automated teller machines (ATM). Like an ordinary savings account balance, this account’s balance is covered under deposit insurance . Also known as money market deposit account (MMDA).