The Apple Lossless Audio Codec (ALAC) is an audio codec developed by Apple and supported on iPhone, iPad, most iPods, Mac and iTunes. ALAC is a data compression method which reduces the size of audio files with no loss of information. A decoded ALAC stream is bit-for-bit identical to the original uncompressed audio file.
FLAC has not taken off. Hopefully ALAC has a brighter future. And now that it's open source pro audio apps can start to support them. Imagine your Pro Tools and Logic Pro session folders taking half the space on your hard disk or that huge sample library that you store on your computer halved.