In general, "bootlegs" such as would be featured on e.g., Lossless Legs or archive.org come in a few types:

Audience (AUD) - recorded by someone with a recorder in the audience.

Soundboard (SBD) - recorded by someone with access to the concert soundboard.

Matrix - Generally, some combination of the above to e.g., patch missing spots or to mix in a desired amount of crowd noise.  

Broadcast (FM) - Something captured off of a radio, television, or internet broadcast.

I actually thought of it while I was adding a bootleg and "broadcast" caught my eye.