Relationship between quantity of inputs a firm uses and the quantity of outputs it produces.
Q = Af(K, L, land)
A = technology (assume it's 1 unless explicitly mentioned)
K = physical capital (a firm's funds are used to buy this, a factor of production: machinery, buildings, vehicles, anything used in order to produce something else, intangible (software, trademarks, brands, etc.))
L = labor (hours or people)