[…] let's say the flop comes 9-9-8, with the open pair on top. One player has J-T-9-8 for the overfull—9s full of 8s for the nut full house—while another player has 8-8-7-6 for 8s full of 9s and the "underfull". The player with the underfull is both getting smashed and drawing dead.
Source: wiktionary