The term fleet media refers to the placement of advertisements on the side of trucks, vans, and other forms of transportation that form part of a commercial fleet.
The crucial difference is that fleet media, like any other form of advertising, is commercially available.
Equally if a delivery/logistics company were to sell advertising space on its delivery vans this would be fleet media.
The only claim that fleet media can make to targeting is that the location of the vehicle in question is potentially limited geographically.
It is something of a stretch to consider this targeting even if a vehicle is limited to a singles state, or area of the country, but occasionally this kind of thing is quoted anecdotally as a targeting effect.