Progressive coding

(Or "interlacing") An aspect of a graphics storage format or transmission algorithm that treats bitmap image data non-sequentially in such a way that later data adds progressively greater resolution to an already full-size image. This contrasts with sequential coding. Progressive coding is useful when an image is being sent across a slow communications channel, such as the Internet, as the low-resolution image may be sufficient to allow the user to decide not to wait for the rest of the file to be received. See also progressive/sequential coding.

Free Online Dictionary of Computing