Girls bend their knees as a gesture of greeting when curtseying. When a person rests his or her weight on one or both knees, the posture is called kneeling. Kneeling is a posture of submission and also used as a posture for punishment.
The knee in spanking
In a variant of the bent-over position, the spankee puts their hands on their knees.
"Over the knee" is a well-known and popular spanking position in which, despite its name, the spankee is not laid over the spanker's knee but over the seated spanker's thigh (see also lap). The same holds for the over-one-knee position.