Are you asking about Bearshare program or LW? I noticed you also posted in the LW spanish section.

Quality represents your chances of a successful downld.

Bit rate refers to an audio song's bit rate encoding. For mp3's this might be between 1 to 320 kbps. For m4a files it might go much higher. If they are higher then they're probably lossless compressed; as good as the original.