Atman (probably from Skt. an “to breathe”) is a concept found in Hinduism, particularly in the school of Advaita Vedanta, that may be roughly understood as the “soul.”¹
In the Upanisads, the Atman is eternal, all-knowing and cannot be destroyed. The lower-case version atman, translated from the Sanskrit, usually refers to the personal soul. Meanwhile, the upper-case Atman is the universal soul, said to be identical with the Brahman. And this is where the Hindu understanding of soul arguably differs from say, the Christian view.
The aim of mystical Hinduism is the joining of the personal atman to the universal Atman-Brahman. Just what this implies depends on the particular Hindu thinker one subscribes to.
Having said that, we have to remember that there are different schools of Hindusim (see Related Posts, below), and it’s arguably a simplification to lump the diverse strands of Hindu philosophy and experience into a homogeneous package, as so many overzealous Christian apologists seem to do.
By the same token, it’s equally simplistic to equate potentially diverse Christian mystical experiences with their Hindu counterparts as if all were identical. This seems an unjustifiable tendency among some New Age enthusiasts who use the term “Christ Consciousness” to denote an alleged ultimate awareness said to be qualitatively identical to all other forms of revelatory and mystical encounters.
In fact, whenever people distort the lightness and beauty of Christian spirituality by cherry picking aspects of the Bible to apparently support their mixed up view of religion, a red flag goes up in this writer’s mind. To me it signals that the person really doesn’t know what they’re talking about.
¹ This entry focuses on the Hindu view of atman, mostly because I took three graduate courses at Santiniketan, W. Bengal involving the topic. Although the courses covered Buddhist and Jain variations of the concept, two of the three credits earned focused on the Bhagavad Gita, so my memory is strongest regarding the Hindu understanding. For the Buddhist and Jain variations, see http://en.wikipedia.org/wiki/Atman