Double articulated bus. Photo: Van Hool
An articulated bus is a bus with one or more trailers, that have their chassis connected by (a) turntable joint(s), and their bodies by a folding polyester bellow(s).
This type of bus is also known as accordion bus, harmonica bus, jointed bus, or bendy bus, all because of the shape of the bellow and the fact that the design of the turntable joint allows for sharp turns.
It is more common for city buses and regional transit buses to be extended by articulation, but articulated charter buses, entertainer buses, etc, etc, do exist also. Therefore we do not consider an articulated bus to be a separate bus type. Used vehicles should be looked for/advertised as city bus, regional transit bus, charter bus, etc, etc.
See all bus type definitions.
Articulated double decker charter bus before its conversion to entertainer bus for jumbocruiser.com
Bellow and trailer.