In economics, what is the inflation-adjusted interest rate called?

The real interest rate is the interest rate adjusted for inflation.

It measures the change in purchasing power associated with borrowing or saving. A commonly used approximation is the nominal interest rate minus the inflation rate. For example, a 6% nominal rate alongside 2% inflation implies an approximate real rate of 4%. The exact Fisher equation uses compounding: one plus the nominal rate equals one plus the real rate multiplied by one plus inflation.

Borrowers and lenders care about real rates because money received or repaid later may buy a different quantity of goods and services. A positive real rate generally rewards saving in purchasing-power terms, while a negative real rate can make borrowing attractive and reduce the real burden of existing debt.

The nominal rate is the percentage stated in a loan or account agreement before inflation adjustment. Expected real rates use anticipated inflation, whereas ex post real rates use inflation that actually occurred. Confusing those two can lead to incorrect conclusions about financial conditions.