The motion picture industry convention assigns a value of 1.0 to the image’s height, thus, an anamorphic frame is described as 2.40:1 or 2.40.
In American cinemas, the common projection ratios are 1.85:1 and 2.40:1.
1.33:1 was used for all cinema films until the 1950s. By a strange coincidence 1.33:1 is the screen ratio of standard television broadcasts.
When television became a threat to movie audiences, Hollywood gave birth to a large number of wide-screen formats: Cinemascope, Todd-AO, and VistaVision (to name just a few). During the 1950s the 1.85:1 aspect ratio became one of the most common cinema projection standards in the U.S.A.
So which result on your TV... I think some pictures are better like 10 pages of (hard) technical explanation:
Most video DVDs include a data marker that automatically selects the best aspect ratio for the video to be displayed. This way, the full area of a 16:9 widescreen TV set can be utilized without changing the resolution of video DVDs. However, sources wider than 16:9 (e.g., 1.85:1 or 2.35:1 aspect ratios), must still be letterboxed to the 16:9 frame with black bars (like show on pictures).