FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, 
but lossless, meaning that audio is compressed in FLAC without any loss in 
quality. This is similar to how Zip works, except with FLAC you will get much 
better compression because it is designed specifically for audio, and you can 
play back compressed FLAC files in your favorite player (or your car or home 
stereo) just like you would an MP3 file.

FLAC stands out as the fastest and most widely supported lossless audio codec, 
and the only one that at once is non-proprietary, is unencumbered by patents, 
has an open-source reference implementation, has a well documented format 
and API, and has several other independent implementations.