Source : Free On-Line Dictionary of Computing

average seek time
     
         The mean time it takes to move the {head} of a {disk
        drive} from one {track} to another, averaged over the source
        and destination cylinders.
     
        The average seek time gives a good measure of the speed of the
        drive in a multi-user environment where successive read/write
        request are largely uncorrelated.
     
        Ten ms is common for a {hard disk} and 200 ms for an
        eight-speed {CD-ROM}.
     
        (1997-07-22)