Interest rate: ------ of the principal that must be paid throughout the life of the note/bond

What is the blank?

The textbook evidence around this answer says: "The amount of each interest payment can be calculated from the face amount, the interest rate, and the number of payments per year, which are all stated in the debt contract. (The interest rate identified in the contract goes by various names, including stated rate, coupon rate, and contract rate.) Recall the formula for calculating interest"