The phrase "A is A" represents the law of identity.
Everything is specific in nature and is equal only to itself.
Philosophy and Logic
Law of Identity: In logic, this idea was first detailed by Aristotle in his work Metaphysics, stating that a thing is what it is, represented by A = A. When an object exists, it has a set of traits that make it… what it… is.
Ayn Rand: The novelist and philosopher used "A is A" as the foundation of the philosophy of Objectivism, meaning reality is real, facts are facts, and things do not change just because we wish them to change.
Everyday Meaning
Self-Containment: It means a thing cannot be its own opposite at the same time. A dog is a dog, a rock is a rock, and you are you.
Truth: It is a way to say that reality has a fixed identity that we must accept to make sense of the world.
Facts are Facts
A is A
You is You