Basically it's what used to be called a cigarette lighter socket. What can you use it for? Lets see, hook up your portable curling iron, recharge your cell phone, CB radio power, hot coffee mug, heated vest, pants and jacket ( like you would wear on a motorcycle- they come in useful during the winter), recharge your iPod, powered cooler, 12v to 120v inverter, 12v auto heater, 12v travel grille, 12v coffee maker, etc.