Atman, in Hinduism, this may be roughly understood as the "soul."
The Atman is eternal, all-knowing and cannot be killed.
The lower-case atman, usually refers to the personal soul.
The upper-case Atman is the universal soul, said to be identical with the Brahman.
The aim of mystical Hinduism is the joining of the personal atman to the universal Atman-Brahman.