Out-of-home advertising (aka OOH advertising or outdoor advertising) or out-of-home media (aka OOH media or outdoor media) is advertising that reaches the consumers while they are outside their homes. Out-of-home advertising is focused on marketing to consumers when they are "on the go" in public places, in transit, waiting (such as in a medical office), and/or in specific commercial locations (such as in a retail venue). OOH advertising formats fall into four main categories: billboards, street furniture, transit, and alternative.