For Camus, the universe is irrational and meaningless, and yet humans are desperate to find reason and meaning in it. And he call this discrepancy "The Absurd". Once you become aware of "The Absurd", you only have three choices: Return to the cycle of daily life and don't think about it, commit suicide, or his preferred option, rebellion. i.e. accept the absurd and be happy anyway. Because screw the universe for thinking it can control how you feel.