B-pillar

noun

B-pil·lar ˈbē-ˈpi-lər

variants or less commonly B-post

ˈbē-ˈpōst

plural B-pillars also B-posts

: either one of two support posts that connect a vehicle's roof to its body at the rear of the front door

In some extreme cases, usually associated with accidents and subsequent body work, the latch pin on the B-pillar will need to be moved up, down, in or out.—

Mike Allen, Popular Mechanics, November 1998

It's quieter inside than in BMW's last convertible, mostly because the front seatbelts no longer flap in the wind. They are mounted on the seats instead of the B-pillars.—

Natalie Neff, Autoweek, 8 May 2000