A double belly buster is a hand in which you have 2 inside straight draws. Similar to an open ended straight draw (OESD), there are 8 outs to complete your straight draw.
An example is being dealt the hole cards JT when the flop is A-Q-8. Although not open-ended, any King or Nine will complete the nut straight.
EXAMPLE “I was ecstatic to have hit my double belly buster on the river but the other player made a flush.”