Lossy compression is a data compression method that sacrifices some information to achieve an even smaller file size than lossless compression. Lossy compression is most often used on video, audio, and many types of image files. For example, in an MP3, lossy compression can remove parts of the sound file that the human ear can barely hear. By doing this, nearly all of the sound quality is preserved while reducing file size.
Some files types do not support lossy compression at all. If they are compressed in this method, they will not work when decompressed.