"Otk" in the context of porn video tags usually stands for "Over The Knee." It refers to a type of BDSM play or spanking scenario where one person, typically the dominant partner, is kneeling with their head facing the ground and their backside exposed. The submissive partner then positions themselves over the dominant's knee and receives discipline, punishment, or pleasure from being spanked. This position allows for easy access to the bottom's buttocks and provides a power dynamic between both partners