A step van is an extremely rugged commerical van, used a lot by delivery and construction workers. The roof of a step van is high enough to allow a person to stand inside.
The step van gets its name from the fact that there are a couple of steps to climb up when entering from the sliding driver's side or passenger's side doors.
Step vans are often used by delivery companies, due to their truly massive cargo capacity. The United Parcel Service (UPS) uses them exclusively.
The body and chassis of a step van are aluminum. Since aluminum bodies are not as suceptible to damage from the corrosive action of water and road salt, a step van can remain in service for a very long time without any rust or corrosion problems.
One of the coolest step vans I've ever seen was a carpenter's mobile workshop, complete with a bench, various shiny power tools, dust collector system, and even air conditioning.