[Bodhi]

Yeah, that's a bad beat that would win me a 7.5k jackpot at the local cardroom.

I think you understand that notion already. A hand that's a big favorite loses to the underdog; that's a bad beat. For example, KK vs QQ, a lot of preflop raising, and a Q flops, or hits on the turn or river. That's a bad beat.

Sometimes we use the term for emphasis when someone played unprofitably to hit their longshot draw against the favorite. For example, someone holding 22 calls a flop bet in a small pot and turns a set. Not only is that terrible play, but your buddy will turn to you and say, "Man, that's a bad beat!"