Original Aspect Ratio. Typically, that would be 2.35 instead of 1.78 for 16x9. OAR fans will accept letterboxing on their 16x9 displays. Lots of people don't, and so they make a 1.78 out of the 2.35. Luckily, as time has passed, I think the full frame 16x9 versions are going away, and more people are accepting of the OAR and its letterboxing