The bank in a game of poker is a little similar to the conventional one that exists in the real world where deposits and withdrawals are made and paid to various people. There is only a slight difference with the monetary roles played by both types with such differing factors like interest rates. A bank in poker refers to the person who is made to account for the numerous transactions that go on before, during and after the game.
The main duties of that person who also answers to the name - house, is keeping tabs on the buy-ins, distributing the chips to poker players, calculating the figures involved during the course of the game, and dishing out payments to the game's winners after the playing sessions are over. When bets are made and games are played, there are certainly going to be those who will come out on top including the losers as well, the "bank" is always on hand every step through the game to make payments accordingly.