What is the name given to energy that isn't being used?

The energy that isn't being used is commonly referred to as "idle energy" or "standby energy." This energy remains in a system or device but is not actively contributing to work or output, often resulting in wasted resources. In the context of electricity, it can also be termed "phantom load" or "vampire energy," as it represents power consumed by devices while they are turned off or in standby mode.