FLAC-HD is a high resolution audio format for audiophiles to enjoy more than three times the fidelity of a standard audio CD. Typically Live Bruce Springsteen FLAC-HD files are recorded at 24 bit / 48 KHz for maximum fidelity. Follow the instructions in this FAQ for standard FLAC playback to listen to FLAC-HD files.
For more information on 24 bit audio, please see this excellent FAQ
FLAC-HD files can not be played on iTunes without conversion but can also be played on other players like VLC Media player.
ALAC-HD files are native to iTunes but can also be played on other players like VLC