This refers to the use of any part of the mouth to sexually stimulate the male or female genitalia. Oral sex may be part of foreplay, after intercourse to help some women to climax in particular, or performed as a sexual act on its own.
An orgasm is the peak of sexual stimulation. Sexual tension builds up when we get aroused. This tension is released during an orgasm, when the muscles in and around the vagina rhythmically contract for females, and semen is ejaculated by men, accompanied by an intense sensation that is pleasurable and satisfying.