Lossless data compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. By contrast, lossy data compression permits reconstruction only of an approximation of the original data, though this usually improves compression rates (and therefore reduces file sizes).
Lossless data compression is used in many applications. For example, it is used in the ZIP file format and in the GNUtool gzip. It is also often used as a component within lossy data compression technologies (e.g. lossless mid/side joint stereo preprocessing by the LAME MP3 encoder and other lossy audio encoders).