FLAC files are lossless and can be as good as, or better than CD quality, but will not play in stand-alone versions of iTunes or Windows Media Player. Read more about FLAC here.
Note: you must use a media player that supports FLAC files to access the meta-data, such as album art, track names, etc.
You will be able to play FLAC files in VLC Media Player, which you can download below:
Download VLC Media Player for Mac here.
Download VLC Media Player for PC here.