Merdian Lossless Packing (MLP)
Meridian's Lossless Packing (MLP) is the main technology behind DVD-Audio. Its lossless compression scheme was groundbreaking and competed favorably with Sony's DSD technology found in the SACD format. MLP is capable of reproducing a master-quality audio presentation in stereo or in 5.1 surround sound from a DVD-Audio disc and a number of other formats. MLP is a music-friendly compression format that helps get more data onto discs of many varieties.
While not used as much now, given the near-demise of the DVD-Audio format, MLP lives on as a major component of Dolby TrueHD.
Lossless compression is works in a similar fashion as "Zip" files on a computer, where the data is compressed, but not of it lost. So when it is unpacked, all the original data can be recovered. Generally, MLP provides a 2:1 level of compression.
This is the opposite of "lossy" compression (like MP3), in which data is left out, and can never be recovered.
For more on MLP, check out the Wikipedia page.