Absurdism is a school of philosophical thought based on the belief that the universe is irrational and meaningless and that the search for order brings the individual into conflict with the universe. As a philosophy, it also explores the fundamental nature of the Absurd and how individuals, once becoming conscious of the Absurd, should react to it.
Absurdism is very closely related to existentialism and nihilism and has its origins in the 19th century Danish philosopher, Søren Kierkegaard, who chose to confront the crisis humans faced with the Absurd by developing existential philosophy.
Absurdism as a belief system was born of the European existentialist movement that ensued, specifically when the French Algerian philosopher and writer Albert Camus rejected certain aspects from that philosophical line of thought and published his essay The Myth of Sisyphus. The aftermath of World War II provided the social environment that stimulated Absurdist views and allowed for their popular development, especially in the devastated country of France.
According to Kierkegaard and Camus, beings looking for meaning in a meaningless world, humans have three ways of resolving the dilemma:
Suicide (both dismiss the viability of this option)
Religious, Spiritual, or abstract belief in a transcendent realm, being, or idea (Camus regarded this solution as “philosophical suicide”) (Kierkegaard stated that a belief in anything beyond the Absurd requires a non-rational but perhaps necessary religious acceptance in such an intangible and empirically unprovable thing)
Acceptance of the Absurd: a solution in which one accepts the Absurd and continues to live in spite of it. (Camus endorsed this solution) (Kierkegaard regarded this solution as “demoniac madness”)
Sources: Merriam Webster, Wikipedia