Shotgun can be a noun or an adjective. As a noun it can mean a type of gun that has a long barrel, a formation in American football, and the front seat of a vehicle. Someone can call shotgun, which means he or she reserved the right to sit in the front seat.
As an adjective, shotgun can either refer to something related to the weapon or to an approach to doing an activity that is not very effective but covers a wide range of options. This second definition comes from how a shotgun works. The gun is not very accurate in hitting a mark. Instead it depends on hitting a wide area at a short range in the hopes of getting the target.
Side note: There are two slang definitions that use shotgun as a verb. One can shotgun an alcoholic beverage by putting a hole in the bottom and letting it drain quickly into one’s mouth. Two people can shotgun when one inhales from a cigarette and then exhales into the other person’s mouth.
In marketing there is the shotgun approach that means to cover a wide geographic or demographic population.
In contrast, there is the rifle approach that means to target a specific audience with all one’s resources.
As a weapon, a rifle is much more accurate and used for long distances.
“Currently when you look at maps for this region it’s pretty much a shotgun approach,” says Sami Tornikoskhi, leader of WWF’s Living Himalayas Initiative based in Thimphu. [The Guardian]