This format removes the top and bottom cropping bars (the "mattes"). It exposes the full vertical image originally captured by the camera lens, filling up a modern 16:9 (1.78:1) television screen.
To understand its appeal, we first need to understand the concept of "open matte." Kill Bill - Vol 1 -2003- OPEN MATTE -1080p Web-...
Do not confuse this with the standard 1080p Blu-ray. The Blu-ray is also 1080p, but it is coded at 2.35:1 with black bars baked in . The Open Matte has those bars removed and the image extended vertically. This format removes the top and bottom cropping