Widescreen does not always mean the same aspect ratio. There are more than a few widescreen aspect ratios. "Widescreen" is more of a generic term.
http://www.dvdaust.com/aspect.htm
http://www.widescreen.org/
Original aspect ratio (OAR)
Original Aspect Ratio (OAR) is a home cinema term for the aspect ratio or dimensions in which a film or visual production was produced—as envisioned by the people involved in the creation of the work. As an example, the film Gladiator was released to theaters in the 2.39:1 aspect ratio. It was filmed in Super 35 and, in addition to being presented in cinemas and television in the original aspect ratio of 2.39:1, it was also broadcast without the matte its original aspect ratio release had.
Criticism
Multiple aspect ratios create additional burdens on consumers and confusion among TV broadcasters. It is not uncommon for a widescreen program to embed a 4:3 commercial. A person owning a 4:3 set would see an image with 2 sets of black stripes, vertical and horizontal (matchboxing). A similar scenario may also occur for a widescreen set owner when viewing 16:9 material embedded in a 4:3 frame. It is also not uncommon that the image is stretched horizontally or vertically. These artifacts can't be dismissed as negligence on the part of program vendors. They could be avoided if the decision about widescreen format standards were taken more seriously. There is good reason for TV screen design to abandon artifacts of the analog era, and start to mimic computer monitors.
Historic and commonly used aspect ratios
* 1.19: "Movietone" - early 35 mm sound film ratio used in the late 1920s and early 1930s, especially in Europe. The optical soundtrack was placed on the side of the 1.33 frame, thus reducing the width of the frame. The Academy frame (1.37) fixed this by making the frame lines thicker. The best examples of this ratio are Fritz Lang's first sound films: M and The Testament of Dr. Mabuse
* 1.25: Commonly used computer resolution of 1280x1024. Native aspect ratio of many LCDs. Also the aspect ratio of 4x5 film photos.
* 1.29: Ratio of US Letter size paper (11:8.5 inches), in landscape format.
* 1.33: 35 mm original silent film ratio, common in TV and video as 4:3. Also standard ratio for IMAX and MPEG-2 video compression.
* 1.37: 35 mm full-screen sound film image, nearly universal in movies between 1928 and 1953. Officially adopted as the Academy ratio in 1932. Still occasionally used. Also standard 16 mm.
* 1.414: Aspect ratio of standard ISO paper sizes (A4, A3, et cetera). Also the square-root of 2.
* 1.5: The aspect ratio of 35mm film used for photography. Wide-aspect computer display (3:2). Used in Apple Powerbook G4 15.2" displays with resolutions of most recently 1440x960. Also the native NTSC DVD-Video resolution, 720x480, although most videos use non-square pixels for a 4:3 ratio.
* 1.6: computer display widescreen (8:5, commonly referred to as 16:10). Used in WSXGAPlus, WUXGA and other display resolutions.
* 1.66: 35 mm European widescreen standard, also Super 16 mm and Japanese HiVision.
* 1.75: early 35 mm widescreen ratio, since abandoned.
* 1.78: video widescreen standard (16:9). Also used in high-definition television One of 3 ratios specified for MPEG-2 video compression.
* 1.85: 35 mm US and UK widescreen standard for theatrical film. Uses approximately 3 perforations ("perfs") of image space per 4 perf frame; films can be shot in 3-perf to save cost of film stock.
* 2.20: 70 mm standard. Originally developed for Todd-AO in the 1950s. 2.21:1 specified for MPEG-2 but not used.
* 2.35 : 35 mm anamorphic prior to 1970, used by CinemaScope ("'Scope") and early Panavision. The anamorphic standard has subtly changed so that modern anamorphic productions are actually 2.39, but often referred to as 2.35 anyway, due to old convention. No recent anamorphic films are 2.35. (Note that anamorphic refers to the print and not necessarily the negative.)
* 2.39: 35 mm anamorphic from 1970 onwards. Sometimes rounded up as 2.4. Sometimes refered to as 'Scope.
* 2.59: Cinerama at full height (three specially captured 35 mm images projected side-by-side into one composite widescreen image).
* 2.76: 70 mm anamorphic (Ultra Panavision). Only used on a handful of films between 1956 and 1964, such as Ben-Hur (1959).
* 4.00: Polyvision, three 35 mm 1.33 images projected side by side. Only used on Abel Gance's Napoléon (1927).
