Good odds simply means that the odds you have to call are better than the odds of making your hand. For example, if you have a flush draw and face an all-in bet on the flop, you will have a roughly 36% chance of making your flush and winning. 36% is a little better than 2:1, so if you have to call a bet of $150 to win $300 or more, you're getting good odds and should call.