A money market deposit account (MMDA) is a type of savings account that is offered by banks and credit unions. 

It is similar to a regular savings account in that it is a low-risk way to save money, but it typically offers a higher interest rate than a traditional savings account.

One of the key features of an MMDA is that it allows you to earn interest on your savings while still having access to your funds.  

This means that you can withdraw money from your MMDA at any time, unlike a certificate of deposit (CD) 

which typically requires you to leave your money in the account for a set period of time in order to earn the highest interest rate.

In addition to offering higher interest rates than traditional savings accounts, MMDAs also typically have a higher minimum balance requirement.  

This means that you will need to maintain a certain balance in the account in order to avoid fees or earn the highest interest rate. 

The specific minimum balance requirement varies depending on the bank or credit union and can range from a few hundred to several thousand dollars.