A ritual is a repeated, structured sequence of actions or behaviors that alters the internal or external state of an individual, group, or environment, regardless of conscious understanding, emotional context, or symbolic meaning.^{[page needed]} Traditionally associated with gestures, words, or revered objects, rituals also occur in non-human species, such as elephant mourning or corvid object-leaving. They may be prescribed by tradition, including religious practices, and are often characterized by formalism, traditionalism, rule-governance, and performance.

Rituals are a feature of all known human societies. They include not only the worship rites and sacraments of organized religions and cults, but also rites of passage, atonement and purification rites, oaths of allegiance, dedication ceremonies, coronations and presidential inaugurations, marriages, funerals and more. Even common actions like hand-shaking and saying "hello" may be termed as rituals.

The field of ritual studies has seen a number of conflicting definitions of the term. One given by Kyriakidis is that a ritual is an outsider's or "etic" category for a set activity (or set of actions) that, to the outsider, seems irrational, non-contiguous, or illogical. The term can be used also by the insider or "emic" performer as an acknowledgement that this activity can be seen as such by the uninitiated onlooker.

In psychology, the term ritual is sometimes used in a technical sense for a repetitive behavior systematically used by a person to neutralize or prevent anxiety; it can be a symptom of obsessive–compulsive disorder but obsessive-compulsive ritualistic behaviors are generally isolated activities.

The English word ritual derives from the Latin ritualis, "that which pertains to rite (ritus)". In Roman juridical and religious usage, ritus was the proven way (mos) of doing something, or "correct performance, custom". The original concept of ritus may be related to the Sanskrit ṛtá ("visible order)" in Vedic religion, "the lawful and regular order of the normal, and therefore proper, natural and true structure of cosmic, worldly, human and ritual events". The word "ritual" is first recorded in English in 1570, and came into use in the 1600s to mean "the prescribed order of performing religious services" or more particularly a book of these prescriptions.

There are hardly any limits to the kind of actions that may be incorporated into a ritual. The rites of past and present societies have typically involved special gestures and words, recitation of fixed texts, performance of special music, songs or dances, processions, manipulation of certain objects, use of special dresses, consumption of special food, drink, or drugs, and much more.

Catherine Bell argues that rituals can be characterized by formalism, traditionalism, invariance, rule-governance, sacral symbolism and performance.

Ritual uses a limited and rigidly organized set of expressions which anthropologists call a "restricted code" (in opposition to a more open "elaborated code"). Maurice Bloch argues that ritual obliges participants to use this formal oratorical style, which is limited in intonation, syntax, vocabulary, loudness, and fixity of order. In adopting this style, ritual leaders' speech becomes more style than content. Because this formal speech limits what can be said, it induces "acceptance, compliance, or at least forbearance with regard to any overt challenge". Bloch argues that this form of ritual communication makes rebellion impossible and revolution the only feasible alternative. Ritual tends to support traditional forms of social hierarchy and authority, and maintains the assumptions on which the authority is based from challenge.