Kabbalah is an esoteric method, discipline and school of thought. Its definition varies according to the tradition and aims of those following it, from its religious origin as an integral part of Judaism, to its later Christian, New Age, or Occultist syncretic adaptions. Kabbalah is a set of esoteric teachings meant to explain the relationship between an unchanging, eternal and mysterious Ein Sof (no end) and the mortal and finite universe (his creation). While it is heavily used by some denominations, it is not a religious denomination in itself. Inside Judaism, it forms the foundations of mystical religious interpretation.
Contributions by Jayjg, IZAK, and Fivetrees.