A swap spread is the difference between the fixed component of a given swap and the yield on a sovereign debt security with a similar maturity. In the U.S, the latter would be a U.S. Treasury security. Swaps themselves are derivative contracts to exchange fixed interest payments for floating rate payments.
Because a Treasury bond (T-bond) is often used as a benchmark and its rate is considered to be default risk-free, the swap spread on a given contract is determined by the perceived risk of the parties engaging in the swap. As perceived risk increases, so does the swap spread.
