It is also possible to define a yield spread between two different maturities of otherwise comparable bonds.
[1] Yield spread analysis involves comparing the yield, maturity, liquidity and creditworthiness of two instruments, or of one security relative to a benchmark, and tracking how particular patterns vary over time.
If that spread widens to 4% (increasing the junk bond yield to 9%), then the market is forecasting a greater risk of default, probably because of weaker economic prospects for the borrowers.
[2] Yield spread can also be an indicator of profitability for a lender providing a loan to an individual borrower.
For example, if a borrower's credit is good enough to qualify for a loan at 5% interest rate but accepts a loan at 6%, then the extra 1% yield spread (with the same credit risk) translates into additional profit for the lender.