Definition of semi-bluff
On one side there is pure bluffing, i.e. betting with a hand that has no chance of being the best hand, and on the other side there is betting because you very often have the best hand. In between is the semi-bluff. semi-bluff is a game made only on flop or on the turn. To talk about semi-bluff, there must be some cards left to come. Usually a player who bets or raises in semi-bluff does so because, on the one hand, he thinks he can get his opponent to fold quite often and, on the other hand, because if he is called, he has a draw to save him.
A classic example of semi-bluff
A player opens the button with KJ in spades. The player in the SB position calls the raise. The player in BB position goes down. The flop comes 2-5-7 with two spades. SB check and the player in the SB position puts the flop. This bet will be considered a semi-bluff. This is not a hard bluff with a hand like T4. With KJ we have one flush draw and two overcards. We will then say that the player has bet a semi-bluff.