Full Idea
When we designate this entity with the term 'Dasein' we are expressing not its 'what' (as if it were a table, house, or tree) but its being.
Gist of Idea
'Dasein' expresses not 'what' the entity is, but its being
Source
Martin Heidegger (Being and Time [1927], p.297), quoted by Kevin Aho - Existentialism: an introduction 2 'Phenomenology'
Book Reference
Aho,Kevin: 'Existentialism: an introduction' [Polity 2014], p.30
A Reaction
Presumably analytic discussions of persons try to be too objective. Heidegger is trying to capture the thought at the heart of Kierkegaard's existentialism. Objectivity and subjectivity are never in conflict. Is there really a different mode of existence?