What type of energy does a watt-hour meter specifically measure?

A watt-hour meter is designed to measure energy consumption in terms of real energy, which is the actual energy used by electrical devices to perform work. This energy is expressed in watt-hours (Wh) and represents the product of power (in watts) used over time (in hours).

Real energy is the component of electrical energy that does useful work, such as lighting a bulb or powering an appliance, and is typically what is billed by utility companies to consumers. The watt-hour meter records this useful energy that is converted into mechanical work, heat, or light.

In contrast, reactive energy refers to energy used in the creation of magnetic fields, which does not perform useful work in a circuit. Apparent energy combines both real and reactive energy, reflecting the total amount of electrical energy flow but not the useful energy usage. Stored energy pertains to energy that is kept in a system (like in batteries) but is not what a watt-hour meter measures during regular household or industrial electrical consumption.