Semi-bluff

A semi-bluff is a bet or raise made with a hand that is probably behind at the moment but still has real outs to catch up, a flush draw or an open-ended straight draw rather than a hand that is already ahead. It wins two separate ways: immediately, if the opponent folds, and later, if they call and the draw completes. A pure bluff only has the first path and is drawing dead the rest of the time, which is what makes a semi-bluff the sturdier play.

Worked example. The pot is 60bb and you semi-bluff raise a flush draw for 40bb:

alpha = 40 / (40 + 60) = 0.4

The raise needs a fold 40% of the time to break even purely as a bluff, exactly like any other bet of that size. Unlike a pure bluff, though, you keep your draw's own equity on top of that whenever you do get called, so the total value of the raise is higher than the alpha figure alone suggests.

Checking keeps the drawing equity but gives up the fold equity entirely, handing the opponent a free card to see the next street at no cost.