Orgasm is the sudden discharge of accumulated sexual tension resulting in rhythmic muscular contractions in the pelvic region that produce intensely pleasurable sensations followed by rapid relaxation. It typically lasts for several seconds. Orgasm is also in part a psychological experience of pleasure and abandon, when the mind is focused solely on the personal experience. It is sometimes called climaxing or coming.

In Masters and Johnson's original research of the human sexual response cycle , orgasm is the third of four stages, occurring after the plateau phase and before the resolution phase. Another widely accepted model of the sexual response cycle, developed by Helen Singer Kaplan, M.D., PhD., involves just three stages: desire, excitement and orgasm.

Orgasms vary from person to person and for each individual at different times. Sometimes orgasm is an explosive, amazing rush of sensations, while others are milder, subtler, and less intense. The differences in intensity of orgasms can be attributed to physical factors, such as fatigue and length of time since last orgasm, as well as to a wide range of psychosocial factors, including mood, relation to partner, activity, expectations, and feelings about the experience.

There are several physiological components of orgasm. First, orgasm is a total body response, not just a pelvic event. Brain wave patterns have shown distinct changes during orgasm, and muscles in many different areas of the body contract during this phase of sexual response. Some people experience the involuntary contraction of facial muscles resulting in what looks like a grimace or an expression of discomfort or displeasure, but it is actually an indication of high sexual arousal.

The most characteristic physical feature of orgasm is the sensation produced by the simultaneous rhythmic contractions of the pubococcygeus muscle (pc muscle). Along with contractions of the anal sphincter, rectum and perineum, the uterus and outer third of the vagina (the orgasmic platform) for women, and the ejaculatory ducts and muscles around the penis for men, this constitutes the reflex of orgasm. The first few contractions are intense and close together, occurring at about 0.8-second intervals. As orgasm continues, the contractions diminish in intensity and duration and occur at less frequent intervals.

Despite the anatomical differences between male and female genitals, orgasms in men and women are physiologically and psychologically, or subjectively, very similar. In fact, studies have been done in which "experts" could not reliably determine gender when reading descriptions of orgasms with all anatomical references removed.

Women have described the sensations of orgasm as beginning with a sense of suspension, quickly followed by an intensely pleasurable feeling that usually begins at the clitoris and spreads throughout the pelvis. The genitals are often described as becoming warm, electric or tingly, and these physical sensations usually spread through some portion of the body. Most women also feel muscle contractions in their vagina or lower pelvis, often described as "pelvic throbbing".

The subjective feeling of orgasm in men has been described quite consistently as beginning with the sensation of deep warmth or pressure that corresponds to ejaculatory inevitability, the point when ejaculation cannot be stopped. It is then felt as sharp, intensely pleasurable contractions involving the pc muscles, anal sphincter, rectum, perineum and genitals. Some men describe this part as a sensation of pumping. Finally, a warm rush of fluid or a shooting sensation describes the actual process of semen travelling through the urethra during ejaculation. It is important to note that orgasm and ejaculation are not one in the same event. Although they typically occur together, a man may have an orgasm without ejaculating.

A major difference between the female and the male orgasmic phase is that far more women than men have the physical capability to have one or more additional orgasms within a short time without dropping below the plateau of sexual arousal. Being multi-orgasmic depends on both continued stimulation and sexual interest. Because neither of these is present every time for most women, multiple orgasms do not occur with every sexual encounter. On the other hand, upon ejaculation, men enter a recovery phase called the refractory period. During this time, further orgasm or ejaculation is physiologically impossible. However, some men can learn to have an orgasm without ejaculating, thereby making it possible to experience multiple orgasms.