Tibetan Monks making a Mandala in an art gallery in Brussels

According to Wikipedia:
"Maṇḍala (मण्डल) is a Sanskrit word meaning "circle." In the Buddhist and Hindu religious traditions sacred art often takes a mandala form. The basic form of most Hindu and Buddhist mandalas is a square with four gates containing a circle with a center point. Each gate is in the shape of a T. Mandalas often exhibit radial balance.

These mandalas, concentric diagrams, have spiritual and ritual significance in both Buddhism and Hinduism. The term is of Hindu origin and appears in the Rig Veda as the name of the sections of the work, but is also used in other Indian religions, particularly Buddhism. In the Tibetan branch of Vajrayana Buddhism, mandalas have been developed into sandpainting. They are also a key part of anuttarayoga tantra meditation practices.

In various spiritual traditions, mandalas may be employed for focusing attention of aspirants and adepts, as a spiritual teaching tool, for establishing a sacred space, and as an aid to meditation and trance induction. According to the psychologist David Fontana, its symbolic nature can help one "to access progressively deeper levels of the unconscious, ultimately assisting the meditator to experience a mystical sense of oneness with the ultimate unity from which the cosmos in all its manifold forms arises."
In common use, 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.