FLAC is a lossless audio format. The quality is usually better than mp3.
SBD = "Soundboard". This means the audio is a professional recording.
Some examples:
- officially released shows (Live In Texas, Road To Revolution, Hybrid Theory Live at Download, ...)
- audio ripped from TV broadcasts (Rock Am Ring 2004, Live 8, ...)
- radio broadcasts (Rock Am Ring 2014, Berlin 2012, Madrid 2008, ...)
- webcasts (Orlando 2000, Kevin and Bean Breakfast Show 2007, ...)