Source : WordNet®

lossy
     adj : characterized by or causing dissipation of energy [ant: {lossless}]

Source : Free On-Line Dictionary of Computing

lossy
     
         A term describing a data {compression} {algorithm}
        which actually reduces the amount of information in the data,
        rather than just the number of bits used to represent that
        information.  The lost information is usually removed because
        it is subjectively less important to the quality of the data
        (usually an {image} or {sound}) or because it can be recovered
        reasonably by {interpolation} from the remaining data.
     
        {MPEG} and {JPEG} are examples of lossy compression
        techniques.
     
        Opposite: {lossless}.
     
        (1995-03-29)