A goal sought by all (most?) Vulcans -- the mental state of complete and total logic, unclouded by emotion. To achieve Kohlinar is to finally purge one's mind of all emotions, leaving one's mind free to think in a perfectly logical manner.
While Vulcans generally pride themselves for their logical behavior and lack of emotion, those who have not achieved Kohlinar are more repressing their emotions than eliminating them. When sufficiently provoked, or when an illness or advanced age compromises their self-control, or when a Vulcan gets horny, the emotions run high.
The Star Trek canon doesn't spend all that much time exploring Kohlinar, and as such it isn't entirely apparent whether it's a matter of brainwashing or an actual mental exercise seriously intended to completely destroy a person's emotions. Star Trek: The Motion Picture depicts the achieving of Kohlinar as a very significant event, as a high priestess (or whatever they're properly called on Vulcan) and her minions preside over a ceremony to award Spock a spiffy medallion for his accomplishment. When he stops her awarding it to him, she mind melds with him to discover he's still got a bit of longing left. This news offends everyone else present, and she unceremoniously drops the medallion on the ground. She and her entourage depart without another word, and Spock scoops it up looking remarkably filled with emotion for a person who almost got an award for shedding them all.
If it is just brainwashing, at least it's socially accepted on Vulcan.