Dasein (German pronunciation: [ˈdaːzaɪn]) is a German word that means "being there" or "presence" (German: da "there"; sein "being"), and is often translated into English with the word "existence". It is a fundamental concept in the existential philosophy of Martin Heidegger, particularly in his magnum opus Being and Time. Heidegger uses the expression Dasein to refer to the experience of being that is peculiar to human beings. Thus it is a form of being that is 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.
In German, Dasein is the vernacular term for "existence", as in "I am pleased with my existence" (Ich bin mit meinem Dasein zufrieden). The term has been used by several philosophers before Heidegger, most notably Georg Wilhelm Friedrich Hegel, with the meaning of human "existence" or "presence". It is derived from da-sein, which literally means being-there/there-being—though Heidegger was adamant that this was an inappropriate translation of Dasein. Dasein for Heidegger can be a way of being involved with and caring for the immediate world in which one lives, while always remaining aware of the contingent element of that involvement, of the priority of the world to the self, and of the evolving nature of the self itself.
The opposite of this authentic self is everyday and inauthentic Dasein, the forfeiture of one's individual meaning, destiny and lifespan, in favour of an (escapist) immersion in the public everyday world—the anonymous, identical world of the They and the Them.
In harmony with Nietzsche's critique of the subject, as something definable in terms of consciousness, Heidegger distinguished Dasein from everyday consciousness in order to emphasize the critical importance "Being" has for our understanding and interpretation of the world, and so on.