The interest rate on international money market futures (IMM futures). It is a money market rate that used as underlying in a futures contract (interest rate futures contract).
The futures contract allows the buyer (holder) to lock in a future investment rate (the IMM rate) today or at a specific incoming date based on an underlying security which is some interest-paying debt instrument.

With an interest rate futures, the lender and the borrower agree to lend and borrow, respectively, a specified amount of money on a predetermined future date. The value of an interest rate futures moves in an inverse proportion to the change in market interest rates.