The pillars on a car are lettered from front to back. A-pillars are the steel pillar between the windshield glass and the front door glass. B-pillars are between front door glass and rear door glass, and C-pillar is between rear door glass and rear window glass. Wagons and SUVs usually have an extra piece of side glass behind the rear doors too, so they have D-pillars.
The "A-pillar applique" is probably the black trim piece above the side wiew mirror. I hope that helped.