Definition of preflop
Preflop means "before the flop". All poker hands start preflop. The dealer asks the blinds to post their respective blinds, then deals the cards to all players. Once all players have received their cards, the preflop round begins. The call will go to the player in Under The Gun (UTG) position. He will have the option of calling (limping) the equivalent of the big blind or raising. As long as all players have not matched the preflop bet, the action will continue. Let's say the UTG player raises to 15???, each player will have to fold if they don't want to call, pay the 15??? if they want to go to a flop or raise again.
There is not always a flop
As we said earlier, all poker hands have preflop action, but not all poker hands necessarily have postflop action. A classic case is when the action is folded (all players fold in succession) until the button raises. At this point, the blinds must pay the raise or take turns raising if they want the action to continue. If both blinds fold, the button will win the pot and there will be no postflop action.