Xvid is a MPEG-4 video codec for PC. Its purpose is to compress video in order to allow for faster transmission over computer networks or for more efficient storage on computer disks. Hence, Xvid can somewhat be seen as a ZIP for video. Xvid removes information from video that is not important for human perception in order to achieve very high compression rates while still keeping very good visual quality. As an example: uncompressed digital video is huge and takes up about 100 GB HD space per hour at PAL resolution. The same video would require just 500 MB per hour when compressed with Xvid at high quality. So Xvid can compress video at ratios of 200:1 and more.
