The screen resolutions
800 x 600 &
1024 x 600 have the aspect ratio 4:3 and this is a standard.
What are the other resolution standards?
For example: Widescreen is 16:9
- Extra Wide
Wikipedia has a great article, with graphics, covering that exact question! Enjoy.
Take any resolution and reduce it like a fraction this will give you the aspect ratio. There is no "standard" for aspect ratios any resolution that that has 16 horizontal pixels for every 9 vertical pixels is 16:9. for example 1920/120=16, 1080/120=9 you get 16:9. 1440×900: 1440/90=16, 900/90=10 you get a 16:10 ratio, your aspect ratio will be your lowest common denominator.
@Ryan gave you a good link. I just wanted to add that the three most common computer monitor aspect ratios are 4:3, 16:9, and 16:10.
4:3 is your classic "square" TV ratio. 16:10 was the original popular widescreen monitor ratio (and highly preferred by some, for its extra vertical space). 16:9 has recently become the most popular widescreen monitor resolution, as it matches that of the common 720p and 1080p TV resolutions for media consumption.
The more cynical among us will also note that 16:9 displays allow manufacturers to make cheaper panels by using the same ones as used for smaller HDTVs, even though 16:9 is often considered inferior for desktop computing beyond simple media consumption.
When a company puts "HD" on its marketing materials, that usually means a resolution of at least 720p, or more commonly 1080p (1920x1080). 1080p monitors are often called "Full HD" by their producers. The line between TVs and computer displays has become much blurrier as of late as far as terminology.