Distribution Center
A distribution center is where larger qualities of products on pallets arriving by rail or truck are split into smaller qualities, then shipped out to locations within a specific geographic area.
So your local Walmart store is tied to a regional distribution center. That distribution center fills up trucks many times a day with cases of items that your local Walmart store needs, not usually pallets.
How goods move from a distribution center to the ultimate destination is going to vary by business. It might be done by employees of the company, independent owner operators, or in company trailers that are pulled by contract carriers like knight-swift.
It is not unusual for distribution centers to ship goods to each other to match the supply of goods with where the demand is located.