display aspect ratio (DAR)
The ratio between an image’s width and height. For example, standard-definition (SD) video typically has an aspect ratio of 4:3. High-definition (HD) video typically has an aspect ratio of 16:9. If SD video is played on an HD display, the image is either stretched, or is appended with black borders on left and right sides (pillarboxing). If HD video is played on an SD display, the image will be squeezed or black borders will appear at the top and bottom (letterboxing).