Variable cost(s)

A variable cost is a corporate expense that changes in proportion to how much a company produces or sells. Variable costs increase or decrease depending on a company's production or sales volume — they rise as production increases and fall as production decreases [Investopedia].
Direct materials are considered a variable cost. Direct labor may not be a variable cost if labor is not added to or subtracted from the production process as production volumes change. Most types of overhead are not considered variable costs.
An example of a variable cost is the resin used to create plastic products; the resin is the key component of a plastic product and so varies in direct proportion to the number of units manufactured. As another example, a business only incurs credit card fees when it sells products to customers that are paid for with a credit card; if there are no sales, then there are no credit card fees.

Sources:

Variable Cost: What It Is and How to Calculate It. Investopedia. Retrieved from: https://www.investopedia.com/terms/v/variablecost.asp#:~:text=Investopedia%20%2F%20Sydney%20Saporito-,What%20Is%20a%20Variable%20Cost%3F,and%20fall%20as%20production%20decrea

Variable cost definition. AccountingTools. Retrieved from: https://www.accountingtools.com/articles/what-is-a-variable-cost.html

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