I would call this an articulated lorry or more probably nowadays an articulated truck. Usually abreviated to "an artic". The term lorry I would normally use for a non-articulated truck (ie: one with a rigid chassis all the way from front to back), which would be a smaller vehicle but too large to be called a van.

So, a semi-trailer's trailer could not be rolled on its own without the tractor as it has no wheels on the front whereas a full-trailer's trailer has wheels at the front and back. Have I got that right? I don't think we differentiate between these in the UK, but I could well be wrong. Anyone know for sure?