Implied spread isolates the credit risk premium embedded in a bond's market price. It's calculated as the bond's implied YTM minus the interpolated benchmark Treasury yield at the same maturity. For example, if a corporate bond's implied YTM is 5.5% and the 10Y Treasury yields 3.5%, the implied spread is 200bp. Traders prefer quoting spreads over absolute yields because spreads isolate the bond-specific credit risk, while YTM mixes credit and rate risk. If Treasury yields rise 50bp and a corporate's YTM rises 50bp, the spread is unchanged — meaning credit risk didn't move, just the rate environment. Implied spread is especially useful when market prices move but you want to understand if credit perceptions changed.