The top pic is just a truck. The bottom one is a semi truck (no bed/box) pulling a trailer. Or a tractor trailer.
Top one is a Box Truck, used to own one with a lift on the back.
A “Semi” is a semi tractor-semi trailer. I used to break and load for Carstensen Freight Lines in the summers when I was in college. The Spotter even let me weigh a load one time before I graduated (way back when), he even let me back it up to park it.