The roof support structure on either side of a vehicle's windshield. On a typical sedan, additional pillars are located between the front and rear doors (B pillar) and on either side of the rear window (C pillar). In SUVs, minivans and wagons with extended cargo areas, the C Pillar is the vertical structure behind the rear door while the vertical supports at the rear of the vehicle are called D pillars.
Coupes with no fixed B pillars are often called hardtops. The Mercedes-Benz S-Class Coupe is an example of a modern hardtop. They are becoming increasingly rare, however, due to the additional engineering involved in meeting side impact crash standards without a fixed central pillar.