vehicle which has a pivoting joint in its construction
An articulated vehicle is a vehicle which has a pivot joint. This allows the vehicle to turn more sharply.
There are many kinds of articulated vehicles: buses, trams and trains may be articulated. Steam locomotives were sometimes articulated so the driving wheels could pivot around turns. In fact, the whole idea of a train is an articulated set of vehicles which run along a track.
Any vehicle towing a trailer could be described as articulated. The term (UK) of "articulated lorry" refers to the combination of a front part which pulls (the "tractor") and a rear part which follows (the "trailor"). In American English, these may be called semi-trailer trucks..