A flat surface on which outdoor advertisements are posted
Karen ... [PAR] We can barely turn a corner without seeing some billboard advertising some ... 
large billboards, it can be applied to anywhere there is a flat surface such as 
buses ... billboards is not all good; some cities are banning this new technology 
due to... [DOC] [TLE] Flat or simple curved surfaces (long term) - MACtac [PAR] Long term outdoor advertising or promotion on flat or curved surfaces.