What is yard mule experience?

Yard mule experience means you know how to operate a yard mule, also called a yard tractor. Yard drivers use yard mules to move tractor trailers to and from loading docks around a truck yard. Someone with yard mule experience can hook up a yard tractor to a trailer, drive it through tight spaces in the truck yard, and park the trailer safely in tight spaces, like backing the trailer up to a loading dock in between other parked trailers.