Monocoque construction
Also known as unibody or unitary construction. Early cars had their bodies bolted on to a separately-built chassis framework, with all the weight supported by the chassis, but a monocoque distributes the load better around the structure. It gives greater rigidity than a body-on-frame structure, thus improved ride comfort, refinement and precise handling, but is not thought to be so rugged: many hardcore 4x4s and pick-ups are still body-on-frame, though most new SUVs and even the latest Range Rover have now shifted to monocoque design.
The first monocoque car was the 1923 Lancia Lambda, but it was the 1934 Citroen Traction Avant that really popularised the concept.