An amortizing fixed-for-floating-rate swap with a fixed rate above the market rate for a constant notional principal swap, and an amortization rate that decreases as rates rise and increases as rates fall. The most common variety is a mortgage replication swap. Also called LIBOR Index Principal Swap (LIPS). Compare with Index Amortizing Swap. See Amortizing Swap, Index Allocated Principal (XAC) Bond, Mortgage Replication Swap.