Nipple clamps are a sex toy that squeeze erect nipples to restrict the blood flow and increase arousal. They are most often used on women but can be used on men. The nipples are highly sensitive and are considered an erogenous zone, especially in women. Those who enjoy nipple clamps find that the painful pinch increases sexual stimulation.
Nipple clamps are often associated with BDSM because of the pain/pleasure aspect of the toy.