Torture, at least in the BDSM sense, generally means inflicting ongoing pain and suffering. Some writers refer to this form of torture as "exquisite agony" as it inflicts the pain or suffering as a way of achieving one or more of the goals of BDSM. In other words, it's pain that leads to satisfaction or even ecstasy.
Sometimes, and for some people, getting where they want to go requires pain or suffering that takes them to the edge of what they are able to endure. And, indeed, this may very well be the point. Only once they reach their limit of endurance can what blocks them be put or forced aside.