Breath control is the restriction of oxygen for the purpose of heightened sexual arousal and intensified orgasm. Methods of breath control include strangulation, suffocation, and smothering. This practice may be used during consensual sex or masturbation. It is particularly popular in the BDSM community where it is not uncommon for dominants to control their submissives' breathing.
Breath control is also known as erotic asphyxiation or, when it's used on oneself, auto-erotic asphyxiation.