Atman means soul or pure self. The atman is also recognised to be identical with the breath, thus conveying the sense the atman is the vital life essence. In Advaita the atman is said to be identical with brahman, the universal spirit. Hence the atman is the universal self of all beings. Other schools of thought such as Dvaita, Viseshadvaita and Samkhya posit that the atman is an individual self.
The atman should not be confused to be ones personal identity. Rather, the atman is the ultimate reality underlying ones phenomenal identity. In Yoga this phenomenal identity is known as the [I]ahamkara[/I], literally meaning the constructed and false self. When one attains the goal of Yoga by dissolving the ahamkara, they directly experience the atman.