Apple Lossless Audio Codec - ALAC
Apple Lossless Audio Codec (ALAC) is an audio codec developed by Apple for playback on iTunes and QuickTime and on Apple iOS devices, including the iPhone, iPad and iPods. The ALAC data compression method is "lossless," meaning it reduces the size of audio files with no loss of information. When decoded, the ALAC stream is identical to the original uncompressed audio file, bit-for-bit. The Apple Lossless Audio Codec sources are available under the Apache license.
The Apple Lossless Audio Codec is a similar to other lossless codecs including the Free Lossless Audio Codec (FLAC).
See also Common Audio Formats in Webopedia's Did You Know...? section.