An appliance is a tool or device that performs a certain job. Your toaster is an appliance, and so is your dishwasher. Your dog? Not so much.
Most modern homes are full of appliances that perform various useful tasks — or help you perform them. A hairdryer is an appliance that dries your hair, and a television is an appliance that offers hours of mindless entertainment. The earliest meaning of the word was "action of putting into use," from the verb apply, with its Latin root, applicare, which figuratively means "devote oneself to" or "give attention."