My definition of a suckout is any time someone calls a huge bet on the come for -EV getting the money in worse than a 3:1 dog and winning. Usually this means < 4-5 outs on the flop or < 8 outs on the turn.

Technically I would consider a naked flush draw with no overs and no pairs calling a 3/4 or full pot bet on the turn and getting there on the river a suckout.

1 and 2 outters on the flop are bad, on the turn they're worse. Any situation involving runner runner, especially running inside straight cards.

Like I said though, I consider it a bad beat anytime someone gets their money in worse than 70/30 without odds and gets there.