The U on iTunes - Terms
Lossy Compression
A lossy compression method is one
where compressing data and then decompressing it retrieves data
that may well be different from the original, but is close enough
to be useful in some way. Lossy compression is most commonly used
to compress multimedia data (audio, video, still images), especially
in applications such as streaming media and internet telephony.
The advantage of lossy methods over lossless methods is that in some
cases a lossy method can produce a much smaller compressed file than
any known lossless method, while still meeting the requirements of the
application. It is important to note all media storage methods are lossy
when a live event has been recorded. Current recording methods only capture
a small fraction of the total performance.