A-pillar, B-pillar, C-pillar, D-pillar, etc.

An SUV with four pillars.

An A-pillar is a name applied by car stylists and enthusiasts to the shaft of material that supports the windshield (windscreen) on either of the windshield frame sides. By denoting this structural member as the “A” pillar, and each successive vertical support after a successive letter in the alphabet (B-pillar, C-pillar etc.), this naming scheme allows those interested in car design to have points of reference when discussing design elements.

A “pillarless” hardtop vehicle, considered to have two total pillars.

A stretch limo with five pillars.

In the most usual configuration, the C-pillar supports the rear window, however, depending on configuration, the final pillar can be B, D, or even higher in more extreme examples.

Occasionally cars have a break between windows or doors, but have no supporting material in the space. These non-supporting breaks are not considered to be pillars, and are skipped for purposes of the alphabetical naming scheme. With the introduction of monocoque design in automobiles, supporting pillars have become increasingly important, and nearly every visual break in a modern vehicle contains a supporting pillar.