Base Offering Circular – Multifamily 59 Standard Abbreviation Category of Class Definition ARB Ascending Rate DLY Delay DIF Differential DRB Descending Rate EXE Excess FIX Fixed Rate FLT Floating Rate INV Inverse Floating Rate IO Interest Only NPR No Payment Residual PO Principal Only PZ Partial Accrual WAC WAC (or Weighted Average Coupon) Z Accrual IMD Increased Minimum Denomination SP Special