A scream (/skriːm/ ^ⓘ) is a loud/hard vocalization in which air is passed through the vocal cords with greater force than is used in regular or close-distance vocalisation. This can be performed by any creature possessing lungs, including humans.

A scream is often an instinctive or reflex action, with a strong emotional aspect, like fear, pain, annoyance, surprise, joy, excitement, anger, etc.

A large number of words exist to describe the act of making loud vocalizations, whether intentionally or in response to stimuli, and with specific nuances. For example, an early twentieth century synonym guide places variations under the heading of "call", and includes synonyms such as: bawl, bellow, clamor, cry (out), ejaculate, exclaim, roar, scream, shout, shriek, vociferate, and yell, each with its own implications. This source states:

To call is to send out the voice in order to attract another's attention, either by word or by inarticulate utterance. Animals call their mates, or their young; a man calls his dog, his horse, etc. The sense is extended to include summons by bell, or any signal. To shout is to call or exclaim with the fullest volume of sustained voice; to scream is to utter a shriller cry; to shriek or to yell refers to that which is louder and wilder still. We shout words; in screaming, shrieking, or yelling there is often no attempt at articulation. To bawl is to utter senseless, noisy cries, as of a child in pain or anger. Bellow and roar are applied to the utterances of animals, and only contemptuously to those of persons. To clamor is to utter with noisy iteration; it applies also to the confused cries of a multitude. To vociferate is commonly applied to loud and excited speech where there is little besides the exertion of voice. In exclaiming, the utterance may not be strikingly, though somewhat, above the ordinary tone and pitch; we may exclaim by mere interjections, or by connected words, but always by some articulate utterance. To ejaculate is to throw out brief, disconnected, but coherent utterances of joy, regret, and especially of appeal, petition, prayer; the use of such devotional utterances has received the special name of "ejaculatory prayer." To cry out is to give forth a louder and more excited utterance than in exclaiming or calling; one often exclaims with sudden joy as well as sorrow; if he cries out, it is oftener in grief or agony. In the most common colloquial usage, to cry is to express grief or pain by weeping or sobbing. One may exclaim, cry out, or ejaculate with no thought of others' presence; when he calls, it is to attract another's attention.

Another source proposes different implications for some of these terms, stating that "the call is normally addressed to a specific person... and the shout projected to a distant but identifiable target, the holler is emitted to whomever may be within earshot". Whooping is another name given to the same kind of noise making as hollering. This source separately notes that a shout "may be angry or joyous; it may be directed to one person or many; and, sometimes, its purpose may be merely for the satisfaction of release or of hearing an echo".

In psychology, the scream is an important theme in the theories of Arthur Janov. In his book The Primal Scream, Janov claims that the cure for neurosis is to confront the patient with their suppressed pain resulting from an experienced trauma. This confrontation gives birth to a scream. Janov believes that it is not necessary that it heals the patient from their trauma. The scream is only a form of expression of primal pain, which comes from one's childhood, and the reliving of this pain and its expression. This finally appears through the scream and can cure the patient from their neurosis.

Janov describes the primal scream as very distinctive and unmistakable. It is a "strangely low, rattling and involuntary sound. [...] Some people are moaning, groaning and are coiling themselves up. [...] One screams as result of all the other times when it had to stay still, was making fun of, was humiliated or was beaten up". Janov also says that the primal scream has series of reactions; "the patients that could not even say 'piep' at home, suddenly feels powerful. The scream seems to be a liberating experience". Janov noticed this with all his patients. Women who seem to have baby-voices during the therapy are developing with their primal scream a very low voice.

Gregory Whitehead, founder of the Institute for Screamscape Studies, believes that the voice is used to focus the power: "scream used to be a psychological weapon both for you and against your opponent, it raises confidence to the person using it. Creating power with yell is having to affect someone without touching them". In this case screaming is a protective weapon, as also often used by animals, who scream as an expression of power or during fights with another animal.