A digital floor is a floor with a European barrier and a fixed payout. That is, it only matters where the underlying asset is in relation to the barrier on each floorlet’s expiry date.
If on the floorlet’s expiry date the interest rate is below the barrier (i.e., the option is in the money), the fixed payout is activated; if the interest rate is above the barrier (i.e., the option is out of the money), no payout is made.
The annual payout for a digital floor is defined as a specified percentage of the notional defined. Therefore for each fixing that the option is in-the-money the holder receives:
(notional * payout %) * relevant daycount fraction
Any payout is made on the floorlet’s payment date; the premium is always paid upfront.
Advantages of a Digital Floor
A digital floor can be used for speculating if you have a view on the expected direction of the index rate movement.