means A light truck with an open cargo bed at the back, used to haul gear, tools, or anything you can strap down.

from From the verb phrase "pick up" — to lift or gather something — which by the early 20th century had attached itself to small delivery trucks you'd use to pick up and carry loads. The phrase itself joins the old verb "pick" (Middle English picken, to pierce or pluck) with "up," and the truck sense rolled out of America's early automobile age, when a "pick-up" body simply meant one built for grabbing and moving stuff.