Wrong. "Pillarboxing" only refers to thick bars when the image is academy ratio (1.37:1 or narrower), not matted. A film matted at 1.66:1 would be "windowboxed" (A Clockwork Orange) and a 1.37:1 with black bars on all four sides would be pictureboxed (Criterion academy ratio SD DVD's).Jay G. said:The technical term for this matting on the sides is "pillarboxing," as the mattes look like pillars on the sides of the image.
The process Stephen_J_H described, which results in matting on all 4 sides of the film frame, is called windowboxing, although typically the image ends up looking pillarboxed on a WS theater screen.