Breath Control, also known as Breath Play, restricts a person's breathing to increase erotic pleasure and to achieve an unprecedented orgasm.

So it's literally and figuratively about breathtaking sex. In most cases, breath control is part of BDSM play between a dominant and a submissive. In some cases, it's done solo during masturbation. The dom is the one who restricts the submissive's airflow. During breath play, the sub's brain doesn't get enough oxygen, which causes euphoria (very pleasurable, increased stamina), and due to the lack of oxygen, an orgasm is reached sooner during the act and an orgasm is usually much more intense than normal.