Interpolated Spread

Also known as I Spread, interest rate swap spread, swap spread, ISPRD

To calculate the I-Spread investors calculate the difference between a corporate bond yield and the corresponding point on an Interpolated Swap Curve.
This is the difference between the fixed-leg of an interest rate swap and a treasury bond with the same maturity.

This indicates the credit spread relative to the interest rate swaps market.
This nominal spread is the difference between the yield to maturity of a bond and its yield from an appropriate interest rate curve for the same maturity date.

In euro fixed income market there is an additional concern; there are many governments who issue bonds and they have differing yield levels
While some participants may compare credit spreads through looking at bonds relative to government issues from major countries such as Germany or France
It is increasingly common to use the "nation-neutral" euro swap curve as the foundation for companies.

In Europe a different benchmark is used.
In Europe corporate bond market investors do not use treasury bonds as the benchmark, they use what is called the I-Spread (Interpolated Spread)