A mystical or religious experience, also known as a spiritual experience or sacred experience, is a subjective experience which is interpreted within a religious framework. In a strict sense, "mystical experience" refers specifically to an ecstatic unitive experience, or nonduality, of 'self' and other objects, but more broadly may also refer to non-sensual or unconceptualized sensory awareness or insight, while religious experience may refer to any experience relevant in a religious context. Mysticism entails religious traditions of human transformation aided by various practices and religious experiences.
The concept of mystical or religious experience developed in the 19th century, as a defense against the growing rationalism of western society. William James popularized the notion of distinct religious or mystical experiences in his Varieties of Religious Experience, and influenced the understanding of mysticism as a distinctive experience which supplies knowledge of the transcendental.