variable cost

variable cost
That part of cost which varies with the level of output. This is in contrast to fixed costs, which must be incurred for output to be possible at all, and do not depend on its level. It should be noted that this distinction is different from that of variability over time. The price of an input may be stable for years, but it is still a variable cost if the amount used depends on output. The price of another input may be volatile, but it is still a fixed cost if the amount used does not depend on the level of output.