Answer: pass-through rate.

The correct answer is **A** because the coupon rate of a mortgage pass-through security is termed the **pass-through rate**. This rate is lower than the mortgage rate of the underlying pool of mortgages, accounting for servicing and administrative fees. The pass-through rate received by investors is often referred to as 'net interest' or 'net coupon'. - **Option B** is incorrect as the weighted average coupon (WAC) rate is derived by averaging the mortgage rates of all loans in the pool, weighted by their outstanding balances. It does not directly represent the coupon rate of the security. - **Option C** is incorrect because the coupon rate of the security is not the same as the rate on the underlying pool of mortgages; it is adjusted downward for fees, resulting in the pass-through rate.

Author: LeetQuiz Editorial Team