Metered Variable
A metered variable is an optional element of a subscription plan that represents any metric you want to charge for in addition to the base price (or in lieu of a base price). Metered variables track and charge customers based on usage. Some examples are for energy consumption, cell phone data/bandwidth, seats/users for software licenses, and trips in car-sharing programs.
Once you add a subscription plan to a product variant, you can define the specific metering/pricing for that variant using metered variable tiers.