A billboard is a large outdoor advertising structure usually set near busy roads, in order to catch the attention of pedestrians and drivers. Billboards were born in 1796, when the invention of lithography made real posters possible and have soon become very popular.
Billboards are very common in modern cities and can be part of them: can you image Piccadilly Circus without its famous and sparkling billboards?
Here's an array of some very creative billboards: