Aspect ratiois a fancy term for "proportion," or the ratio of width to height. for example 4:3 for a computer screen. For instance, if a direction in a software manual tells you to "hold down the Shift key while you resize a graphic in order to maintain the aspect ratio," it simply means that if youdon'thold down the Shift key you will stretch the image out of proportion.
Some combinations of computers and printers have trouble maintaining the correctaspect ratio when the image goes from the screen to the printer, or when the image is transferred from one system to another, so the aspect ratio can be an important specification to consider when choosing hardware.
The aspect ratio of the screen determines the most efficient screen RESOLUTIONS and the most desirable shape for individual PIXELS, all of which may have to change upon the introduction of HIGH DEFINITION TELEVISION.