Billboard

A billboard (archaically a "hoarding" in the UK) is a large outdoor advertising structure (a billing board), typically found in high traffic areas such as alongside busy roads. Billboards present large advertisements to passing pedestrians and drivers. Typically showing large, ostensibly witty slogans, and distinctive visuals, billboards are highly visible in the top designated market areas. Bulletins are the largest, most impactful standard-size billboards. Located primarily on major highways, expressways or principal arterials, they command high-density consumer exposure (mostly to vehicular traffic). Bulletins afford greatest visibility due not only to their size, but because they allow creative "customizing" through extensions and embellishments.

Example of billboard

http://en.wikipedia.org/wiki/File:Times_Square_1-2.JPG