Image resolution is the total pixel size of a bitmap image. For example, 720 x 486 for NTSC video output. Display resolution is the number of pixels in 1 inch on the screen. Display resolution is measured in pixels per inch (ppi). Most monitors have a display resolution of about 72 ppi. If your output is for print, consider a display resolution of around 300 ppi.
To set the pixel aspect ratio, see Set the resolution and pixel aspect ratio.
The terms pixels per inch (ppi), and dots per inch (dpi) are often interchanged freely. Pixels per inch, however, applies only to screen resolution, which display images in pixels. Dots per inch, applies only to paper-based images, which are printed with dots of color.