WordNet (r) 3.0 (2006):

lossy
    adj 1: characterized by or causing dissipation of energy [ant:
           lossless]

The Jargon File (version 4.4.7, 29 Dec 2003):

lossy
 adj.

    [Usenet]

    1. Said of people, this indicates a poor memory, usually short-term. This
    usage is analogical to the same term applied to data compression and
    analysis. ?He's very lossy.? means that you can't rely on him to accurately
    remember recent experiences or conversations, or requests. Not to be
    confused with a ?loser?, which is a person who is in a continual state of
    lossiness, as in sense 2 (see below).

    2. Said of an attitude or a situation, this indicates a general downturn in
    emotions, lack of success in attempted endeavors, etc. Eg, ?I'm having a
    lossy day today.? means that the speaker has ?lost? or is ?losing? in all
    of their activities, and that this is causing some increase in negative
    emotions.


The Free On-line Dictionary of Computing (30 December 2018):

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)