Definition of hole card
The hole cards are the cards in the hole. What we mean by cards in the hole, on Hold’em for example, are the two hidden cards that each player receives before flop. The 7 total cards a poker player can use if the hand goes to the river are the flop (3), the turn (1) the river (1) and the hole card (2). These cards must be hidden until the time of the flip. If all players have folded and you win the default prize pool, you do not have to show your hole card.
Showing your hole cards in a bluff?
As we said before, if all players fold before us, we will win the default prize pool. At that point, we can discard our cards without showing them. But if for example we call a big bluff that works, should we show our hole cards or not? Most of the time we don't. Poker is a game of incomplete information and when you show your cards to your opponents, they get free information about you. If you want to show your hole cards in a hand, make sure you have a good reason to do so.