At Mudcat, "BS" (bullshit) means non-music discussions and personal chit-chat. Those who have sensitivities can call it "breeze-shooting," I suppose.

If you don't want to see the non-music discussions, you can bookmark and use the BS filter:
http://www.mudcat.org/threadsnot.cfm?Title=BS:

I go through thread titles every day or two and drop or add the BS designation and other thread title tags as appropriate. I dropped the BS designation from most of the threads listed above.

-Joe Offer-