The "Theatre of the Absurd" plays have some of the same ideas that are found in the philosophy (a way of thinking) called existentialism. Existentialism is very different from many other "philosophies". Most religions and philosopies say that human life has a meaning (or a purpose). The philosophy of existentialism is that human life does not have a meaning (or a purpose). When something has no meaning, it is "absurd". (absurd means means silly and meaningless.)