What do we call energy converted into a form a device was NOT designed for?

When energy is converted into a form that a device was not designed to utilize, this is referred to as wasted energy. Devices are generally engineered to convert energy efficiently for a specific purpose, such as a light bulb converting electrical energy into light. However, some of the energy may be lost in the process as heat or sound—forms that the device does not effectively use for its intended function. This loss of useful energy represents wasted energy, indicating that not all the energy input is converted into the desired output.

The other terms do not accurately describe this scenario. Unused energy typically refers to energy that is available but not utilized at all. Renewable energy denotes energy sources that can be replenished naturally, such as solar or wind power. Conserved energy relates to the principle of energy conservation, wherein energy cannot be created or destroyed but can change forms. Thus, the most appropriate term for energy that is not put to useful work is indeed wasted energy.