The breakeven inflation rate represents a measure of expected inflation implied by the difference between 5-Year Treasury Constant Maturity Securities and 5-Year Treasury Inflation-Indexed Constant Maturity Securities. The latest value implies what market participants expect inflation to be in the next 5 years, on average.
Constant maturity is an adjustment for equivalent maturity, used by the Federal Reserve Board to compute indexes based on the average yield of various Treasury securities maturing at different periods.