variable factor input
variable factor inputa FACTOR INPUT to the production process that can be readily varied in the SHORT RUN so as to expand or reduce output within a plant of fixed size. Variable inputs include raw materials, heating and lighting. Variable costs are equal to the quantities of variable inputs used, multiplied by their prices. See also FIXED FACTOR INPUT, RETURNS TO THE VARIABLE FACTOR INPUT.
Collins Dictionary of Economics, 4th ed. © C. Pass, B. Lowes, L. Davies 2005