"Absurd" originally means "out of harmony," in a musical context. Hence its dictionary definition: "out of harmony with reason or propriety; incong… - Martin Esslin

The "Theatre of the Absurd" has become a catch-phrase, much used and much abused. What does it stand for? And how can such a label be justified? Perhaps it will be best to attempt to answer the second question first. There is no organised movement, no school of artists, who claim the label for themselves. A good many playwrights who have been classed under this label, when asked if they belong to the Theatre of the Absurd, will indigniantly reply that they belong to no such movement — and quite rightly so. For each of the playwrights concerned seeks to express no more and no less his own personal vision of the world. Yet critical concepts of this kind are useful when new modes of expression, new conventions of art arise.

The "poetic avant-garde" relies on fantasy and dream reality as much as the Theatre of the Absurd does; it also disregards such traditional axioms as that of the basic unity and consistency of each character or the need for a plot. Yet basically the "poetic avant-garde" represents a different mood; it is more lyrical, and far less violent and grotesque. Even more important is its different attitude toward language: the "poetic avant-garde" relies to a far greater extent on consciously "poetic" speech; it aspires to plays that are in effect poems, images composed of a rich web of verbal associations. The Theatre of the Absurd, on the other hand, tends toward a radical devaluation of language, toward a poetry that is to emerge from the concrete and objectified images of the stage itself. The element of language still plays an important part in this conception, but what happens on the stage transcends, and often contradicts, the words spoken by the characters. In Ionesco's The Chairs, for example, the poetic content of a powerfully poetic play does not lie in the banal words that are uttered but in the fact that they are spoken to an ever-growing number of empty chairs.

The Theatre of the Absurd … can be seen as the reflection of what seems to be the attitude most genuinely representative of our own time.  The hallmark of this attitude is its sense that the certitudes and unshakable basic assumptions of former ages have been swept away, that they have been tested and found wanting, that they have been discredited as cheap and somewhat childish illusions. The decline of religious faith was masked until the end of the Second World War by the substitute religions of faith in progress, nationalism, and various totalitarian fallacies. All this was shattered by the war.