This document defines and discusses various forms of outdoor advertising. It begins by defining outdoor advertising as any advertising done outside that publicizes business products and services. It then describes common forms of outdoor advertising such as billboards, gantry advertising, street furniture advertising, transit advertising, and guerrilla advertising. Billboard advertising contributes nearly 60% of revenues to outdoor advertising and allows for high-impact, customized messages. Gantry advertising involves sign assemblies mounted on overhead supports along highways. Street furniture advertising uses displays on sidewalk items like bus shelters and benches. Transit advertising appears on vehicles like buses, taxis, subways and trains. Guerrilla advertising promotes products and services unconventionally with little budget through memorable personal attention-grabbing techniques