In poker, when you hold a strong starting hand and raise a lot of money to see the flop, only to have not matched any cards when seeing the flop making your hand completely useless.
Starting hand of A/K. You raise double the blinds, someone else raises double that, you raise again or go all in because you're pot committed.
The dealer turns over the first three cards (flop) and it's 5/2/J all of suits other than the ones in your hand. Probably giving the other guy a really strong hand against you and effectively costing you all your money.
That, my friends, is getting flop nobbed (a Flop Nob).
Common usage: "Hey man, the tables were rough last night, I was constantly getting Flop Nobbed!"