When one says something is 'God' one has to define what is meant by 'God'. If one cannot define 'God', there is no point is saying that one is a theist or an atheist. It is a false description of what a person is. Similarly if one cannot define 'Brahman' one cannot say one is an advaitist who believes in Brahman. or Atman for that matter.
I had an idea of what God should be like and my experience was that the Entity I tried to correspond with was nothing like what I expected a God to be, so I am not a theist or an atheist.
@AJay defines Brahman as Consciousness so he has an understanding of what he is relating to, in terms of his meditation or awareness. Personally, I have no evidence that Brahman is Consciousness either. So I do not subscribe to this classical advaita in the way ajay0 understands it.
@Aupmanyav defines Brahman as physical energy and he is non-dual with this entity so he has his own advaita.
I only know the 'universe' the Hindu term for which I feel is Brahman; of which I am an indivisible part of so my philosophy is to be at one with the universe, as the only truth that is knowable. This raises the question of what are the properties of the universe. I do not know yet. Does it have consciousness that is protective towards the seeker of truths and practitioners of truth accommodation and thereby generates awareness and security for them? Possibly. Is that the definition of God? Who knows?
I am therefore a person who describes himself as a satya-advaitist, namely some one who wishes to be at one with the truth he discovers and lives by that truth in terms of truth accommodation.