When thoughts cease, who are you? An utter emptiness, nothingness, no-thingness. It is because of this that Buddha has used a strange word. Nobody has ever done such a concept before, or since. The mystics have always used the word “self” for the interior-most core of your being. Buddha uses the word “no-self.” And I perfectly agree with him. He is far more accurate, closer to truth. To use the word “self” - even if you use it with a capital “S,” does not make much difference. It continues to give you the sense of the ego. And with a capital “S,” it may give you an even bigger ego.
Buddha does not use the words atma, atta - “self.” He uses just the opposite words: “no-self” - anatma, anatta. He says that when mind ceases, there is no self left. You have become universal, you have overflowed the boundaries of the ego. You are pure space, uncontaminated by anything. You are just a mirror reflecting nothing.