Consists in an imperfect vision of the Supreme Being, and of His infinite perfections.
There are two kinds, one in the natural or ordinary state, which is that of all Christians striving to save their souls; the other in the preternatural, in which the mind is elevated to God and Divine things, joined with an admiring and loving intuition of these.
Saint Augustine defines it as an agreeable admiration of perspicuous truth.
Saint Bernard says it is a certain elevation of the mind dwelling or resting upon God, and tasting the joys of eternal sweetness.
Richard of Saint Victor defines it as the free insight of the mind, dwelling with admiration on the sights or scenes of wisdom.
Saint Thomas tells us it is the simple intuition of Divine truth, and that it terminates in affection and love.
Mystical contemplation is Divine and effective; it enlightens the intellect, and inflames the will in a special manner, and above the human way of acquiring knowledge by reasoning and inference.
New Catholic Dictionary