Consumption function

In economics, the consumption function describes a relationship between consumption and disposable income. Algebraically, this means ${\displaystyle C=f(Y_{d})}$ where ${\displaystyle f\colon \mathbb {R} \to \mathbb {R} }$ is a function that maps levels of disposable income ${\displaystyle Y_{d}}$—income after government intervention, such as taxes or transfer payments—into levels of consumption ${\displaystyle C}$. The concept is believed to have been introduced into macroeconomics by John Maynard Keynes in 1936, who used it to develop the notion of a government spending multiplier. Its simplest form is the linear consumption function used frequently in simple Keynesian models:

...
Wikipedia