The viewable area and shape of a display are referred to as its aspect ratio. For example, most common computer monitors and televisions have an aspect ratio 1.77:1 (16:9). However, ultrawide monitors with the 21:9 aspect ratio (like movies in the theater) are becoming more and more popular with users.
Aspect ratio example
The image below shows the Computer Hope.com logo is displayed with two different aspect ratios that are indicated by their background color. The white area has a shorter width than the entire image, in relation to its height. Therefore, the white section has an aspect ratio of 1.33:1, while the aspect ratio of the entire image is 1.77:1.