Yield spread and spread to mid-swap

Yield spread and spread to mid-swap is a difference between yields on bonds in question and yield on a corresponding base asset (or benchmark) denominated in the same currency and having similar duration; usually the benchmark is government bonds of the country which currency the instrument is denominated in. A spread to mid-swaps (mean values of interest rate swaps) is also calculated. Spreads are calculated to compare investment appeal of different fixed income assets. The key advantage of using IRS or mean mid-swap rates as a benchmark is the fact that they have one reference rate, i.e. calculating a spread to corresponding swaps gives you an opportunity to compare bonds denominated in different currencies.