Dasein is a term in the philosophy of Martin Heidegger. Adopted from the ordinary German word Dasein meaning 'existence', Heidegger used it to refer to the mode of being that he believed is particular to human beings, who are aware of and must confront such issues as personhood, mortality, and the dilemma or paradox of living in relationship with other humans while being ultimately alone with oneself. To put it in simpler terms, it may be understood as a particular way in which humans have consciously felt addressed and challenged by this world.