The configuration of a car body is typically determined by the layout of the engine, passenger and luggage compartments, which can be shared or separately articulated. A key design feature is the car's roof-supporting pillars, designated from front to rear of the car as A-pillar, B-pillar, C-pillar and D-pillar.

The pillars on a car with permanent roof body style are the vertical or nearly vertical supports of its window area or greenhouse—designated respectively as the A, B, C and D-pillar, moving from front to rear, in profile view.