Semi-trailer

Okay kiddo, so a semi-trailer is a big truck that has two parts. The first part is called a "tractor" and it has a engine and driver's seat. The second part is called a "trailer" and it's like a big rectangular box that's attached to the back of the tractor.

The trailer is where all the stuff gets put, like food or toys or furniture. The trailer doesn't have an engine or driver's seat, so it needs the tractor to pull it along the road.

The trailer is usually about 53 feet long and 8 feet wide. It's really big and can hold a lot of stuff. Sometimes, the trailer can be separated from the tractor and loaded onto a train or a ship to travel long distances.

So, that's a semi-trailer - a big truck with two parts, the tractor and trailer. The tractor pulls the trailer, and the trailer carries a lot of stuff.