Interlacing
1. When referring to a computer monitor or other display, interlace or interlacing is a description of how the picture is created. With interlaced the picture is created by scanning every other line, and on the next scan, scanning every opposite line. This allows for a faster refresh rate by having less information during each scan and often allows the display to be sold at a much lower cost. Unfortunately, this may cause flickering or noticeable line movements in some situations.2. When referring to an interlaced graphic image, such as an interlaced GIF or progressive JPEG these are images that are displayed by loading every other line of the image and when at the bottom starting over and loading every opposite line. This image is often only noticed by users with slow slow Internet connections, such as users with a modem connection or when downloading a very large image and will often appear to fade in as it's being loaded.
Also see: GIF, JPEG, Noninterlaced, Progressive, Raster, Refresh, Video definitions