The so-called CobbDouglasProductionFunction is frequently used in simple macroeconomic models. It is

  Y = A * K^a * L^(1-a)

where 

	* Y (yield): what is produced (output)
	* K (capital): machines, real estate, ...; one kind of input
	* L (labour): the other kind of input
	* a (really ''alpha''; elasticity of production): the relative influence of capital and labour input on output
	* A (total productivity of input): there's also productivity of labour (dY/dL) and productivity of capital (dY/dK); sometimes A is also interpreted as "technology".