Orgasm (from Greek ὀργασμός, orgasmos; "excitement, swelling"), sexual climax, or simply climax, is the sudden release of accumulated sexual excitement during the sexual response cycle, characterized by intense sexual pleasure resulting in rhythmic, involuntary muscular contractions in the pelvic region. Orgasms are controlled by the involuntary or autonomic nervous system and are experienced by both males and females; the body's response includes muscular spasms (in multiple areas), a general euphoric sensation, and, frequently, body movements and vocalizations. The period after orgasm (known as the resolution phase) is typically a relaxing experience due to the release of the neurohormones oxytocin and prolactin, as well as endorphins (or "endogenous morphine").

Human orgasms usually result from physical sexual stimulation of the penis in males (typically accompanied by ejaculation) and of the clitoris (and vagina) in females. Sexual stimulation can be by masturbation or with a sexual partner (penetrative sex, non-penetrative sex, or other sexual activity). Physical stimulation is not a requisite, as it is possible to reach orgasm through psychological means. Getting to orgasm may be difficult without a suitable psychological state. During sleep, a sex dream can trigger an orgasm and the release of sexual fluids (nocturnal emission).

The health effects surrounding the human orgasm are diverse. There are many physiological responses during sexual activity, including a relaxed state, as well as changes in the central nervous system, such as a temporary decrease in the metabolic activity of large parts of the cerebral cortex, while there is no change or increased metabolic activity in the limbic (i.e., "bordering") areas of the brain. There are sexual dysfunctions involving orgasm, such as anorgasmia.

The importance of reaching orgasm for sex to be satisfying varies between individuals, and theories about the biological and evolutionary functions of orgasm differ.

In a clinical context, orgasm is usually defined strictly by the muscular contractions involved during sexual activity, along with the characteristic patterns of change in heart rate, blood pressure, and often respiration rate and depth. This is categorized as the sudden discharge of accumulated sexual tension during the sexual response cycle, resulting in rhythmic muscular contractions in the pelvic region. Definitions of orgasm vary, and at least 26 definitions of orgasm are listed in the 2001 journal Clinical Psychology Review.

There is some debate about whether certain types of sexual sensations should be accurately classified as orgasms, including female orgasms caused by G-spot stimulation alone, and the demonstration of extended or continuous orgasms lasting several minutes or even an hour. The question centers around the clinical definition of orgasm, but this way of viewing orgasm is merely physiological, while there are also psychological, endocrinological, and neurological definitions of orgasm. In these and similar cases, the sensations experienced are subjective and do not necessarily involve the involuntary contractions characteristic of orgasm. In both sexes, they are extremely pleasurable and often felt throughout the body, causing a mental state that is often described as transcendental, and with vasocongestion and associated pleasure comparable to that of a full-contractionary orgasm. For example, modern findings support the distinction between ejaculation and male orgasm. For this reason, there are views on both sides as to whether these can be accurately defined as orgasms.

Orgasms can be achieved during a variety of activities, including vaginal, anal, oral, manual, and non-penetrative sex, or masturbation. They may also be achieved by the use of a sex toy or an erotic electrostimulation. Achieving orgasm by stimulation of the nipples or other erogenous zones is rarer. Multiple orgasms (orgasms that occur within a short period of one another) are also possible, especially in women, but they are also uncommon.

In addition to physical stimulation, orgasm can be achieved from psychological arousal alone, such as during dreaming (nocturnal emission for males or females) or by forced orgasm. Orgasm by psychological stimulation alone was first reported among people who had spinal cord injuries. Although sexual function and sexuality after spinal cord injury are very often impacted, this injury does not deprive one of sexual feelings such as sexual arousal and erotic desires.