1. An instrument; such as, an ampere-hour meter, that measures electrical power and totals its measurement with time.
2. A device that measures electric power consumed, either at an instant, as in a wattmeter, or averaged over a time interval, as in a demand meter.

A demand meter is any of several types of instruments used to determine a customer's maximum demand for electric power over a time interval; generally it is used for billing industrial users.