FLAC=Free Lossless Audio Codec
In a nutshell, a clever little software algorythm that allows you to compress music tracks significantly without losing quality. True archive quality in that you can rebuild the original even though it is compressed.
Kind of like Apple Lossless, except it's not a-la-Apple and it's opensource.
All my digital music collection is in FLAC format (As opposed to MP3 or other (IMO) lossy formats)
ROCKbox is a version of opensource firmware that you can run (in parallel if necessary) on your iPod that allows you to play .FLAC format music through the iPod hardware. Basic, but it's not the bell's-n-whistles of the ipod firmware I'm after
Let me know if this doesn't answer your Q's
