Out-of-home advertising (also referred to as OOH) is essentially all type of advertising that reaches the consumer while he or she is outside the home. This is in contrast to broadcast, print, or internet advertising, which may be delivered to viewers out-of-home (e.g. via tradeshow, newsstand, hotel lobby room), but are usually for home or office viewing. Outdoor products are divided among three primary categories: Billboards, street furniture and transit. The most common product in OOH is the billboard. OOH encompasses outdoor advertising but extends to the indoors as well (such as ads in malls).
This is a non-exhaustive list. There are virtually no limits to shape and size of out-of-home advertising media.
Selling advertising space
If a private property owner wants to sell advertising space to one of the outdoor advertising companies ('media sellers') he or she directly approaches the company. A media seller may also approach the owner of an interesting property and make a bid. If an agreement is signed, the media seller erects a structure for displaying the ads and rents out the space to the clients. The world's largest media sellers are JCDecaux, Clear Channel Outdoor, Lamar Advertising and CBS Outdoor.