Corporate bond spreads are an important measure of risk, liquidity and general economic/market conditions. Corporate bond spreads or credit spreads represent the yield above an equal maturity Treasury bond or risk-free rate.
For example, if a 10-year Treasury bond is yielding 3% and a 10-year BBB-rated corporate bond is yielding 5%, the credit spread is 2%.
As corporate spreads get wider, that is an indication of tightening liquidity, higher risk in the market place and/or worsening economic conditions.
You can measure the corporate spreads for all credit