The Is Curve It can easily be detected that there is a As negative relation between interest rate and income. A curve that reflect such a relation is called IS(standing for investment and saving)curve. It represents the equilibrium condition in the product market (see the graph presented in class)The IS Curve • It can easily be detected that there is a negative relation between interest rate and income. A curve that reflect such a relation is called IS (standing for investment and saving) curve. It represents the equilibrium condition in the product market (see the graph presented in class)