Do what I do, Echoes, when I want to know something: look it up on Google! Here is what Wikipedia says (among other things):

Mandala (Sanskrit maṇḍala मंडलः "circle", "completion") is a term used to refer to various objects. It is of Hindu origin [citation needed], but is also used in other Indian religions, such as Buddhism. In the Tibetan branch of Vajrayana Buddhism, they have been developed into sandpainting. In practice, mandala has become a generic term for any plan, chart or geometric pattern that represents the cosmos metaphysically or symbolically, a microcosm of the Universe from the human perspective.

In various spiritual traditions, mandala may be employed for focusing attention of aspirants and adepts, a spiritual teaching tool, for establishing a sacred space and as an aid to meditation and trance induction.