A tragedy is a genre of drama based on human suffering and, mainly, the terrible or sorrowful events that befall a main character or cast of characters. Traditionally, the intention of tragedy is to invoke an accompanying catharsis, or a "pain [that] awakens pleasure," for the audience. While many cultures have developed forms that provoke this paradoxical response, the term tragedy often refers to a specific tradition of drama that has played a unique and important role historically in the self-definition of Western civilization. That tradition has been multiple and discontinuous, yet the term has often been used to invoke a powerful effect of cultural identity and historical continuity—"the Greeks and the Elizabethans, in one cultural form; Hellenes and Christians, in a common activity," as Raymond Williams puts it.

Originating in the theatre of ancient Greece 2500 years ago, where only a fraction of the works of Aeschylus, Sophocles and Euripides survive, as well as many fragments from other poets, and the later Roman tragedies of Seneca; through its singular articulations in the works of Shakespeare, Lope de Vega, Jean Racine, and Friedrich Schiller to the more recent naturalistic tragedy of Henrik Ibsen and August Strindberg; Nurul Momen's Nemesis' tragic vengeance & Samuel Beckett's modernist meditations on death, loss and suffering; Heiner Müller postmodernist reworkings of the tragic canon, tragedy has remained an important site of cultural experimentation, negotiation, struggle, and change. A long line of philosophers—which includes Plato, Aristotle, Saint Augustine, Voltaire, Hume, Diderot, Hegel, Schopenhauer, Kierkegaard, Nietzsche, Freud, Benjamin, Camus, Lacan, and Deleuze—have analysed, speculated upon, and criticised the genre.

In the wake of Aristotle's Poetics (335 BCE), tragedy has been used to make genre distinctions, whether at the scale of poetry in general (where the tragic divides against epic and lyric) or at the scale of the drama (where tragedy is opposed to comedy). In the modern era, tragedy has also been defined against drama, melodrama, the tragicomic, and epic theatre. Drama, in the narrow sense, cuts across the traditional division between comedy and tragedy in an anti- or a-generic deterritorialization from the mid-19th century onwards. Both Bertolt Brecht and Augusto Boal define their epic theatre projects (non-Aristotelian drama and Theatre of the Oppressed, respectively) against models of tragedy. Taxidou, however, reads epic theatre as an incorporation of tragic functions and its treatments of mourning and speculation.

The word "tragedy" appears to have been used to describe different phenomena at different times. It derives from Ancient Greek τραγῳδία "goat song", which comes from τράγος tragos "he-goat" and ᾠδή ōidḗ "singing, ode." Scholars suspect this may be traced to a time when a goat was either the prize in a competition of choral dancing or was what a chorus danced around prior to the animal's ritual sacrifice. In another view on the etymology, Athenaeus of Naucratis (2nd–3rd century CE) says that the original form of the word was trygodia from trygos (grape harvest) and ode (song), because those events were first introduced during grape harvest.

Writing in 335 BCE (long after the Golden Age of 5th-century Athenian tragedy), Aristotle provides the earliest surviving explanation for the origin of the dramatic art form in his Poetics, in which he argues that tragedy developed from the improvisations of the leader of choral dithyrambs (hymns sung and danced in praise of Dionysos, the god of wine and fertility):

Anyway, arising from an improvisatory beginning (both tragedy and comedy—tragedy from the leaders of the dithyramb, and comedy from the leaders of the phallic processions which even now continue as a custom in many of our cities), [tragedy] grew little by little, as [the poets] developed whatever [new part] of it had appeared; and, passing through many changes, tragedy came to a halt, since it had attained its own nature.

— Poetics IV, 1449a 10–15

In the same work, Aristotle attempts to provide a scholastic definition of what tragedy is: