Lossless data compression is a class of data compression algorithms which allows the exact original data to be reconstructed from the compressed data, that is, no data is removed from the original file during compression, and the uncompressed file will be identical to the original prior to compression. For audio archival purposes, if compression is to be used, lossless compression is considered by some to be at a minimum, preferable. Others consider it to be essential.
Lossless compression contrasts with "lossy" data compression. During lossy compression, mp3 for example, data is removed and the decompressed file is not, and will never be, identical to the original. Compression rates with lossy compression are however much greater than those that can be achieved with lossless compression.