The definition, or meaning, of the term "mysticism" has changed throughout the ages
McGinn argues that "presence" is more accurate than "union", since not all mystics spoke of union with God, and since many visions and miracles were not necessarily related to union. He also argues that we should speak of "consciousness" of God's presence, rather than of "experience", since mystical activity is not simply about the sensation of God as an external object, but more broadly about
...new ways of knowing and loving based on states of awareness in which God becomes present in our inner acts.
D.J. Moores too mentions "love" as a central element:
Mysticism, then, is the perception of the universe and all of its seemingly disparate entities existing in a unified whole, bound together by love.
Related to the idea of "presence" instead of "experience" is the transformation that occurs through mystical activity:
This is why the only test that Christianity has known for determining the authenticity of a mystic and her or his message has been that of personal transformation, both on the mystic's part and—especially—on the part of those whom the mystic has affected.
Belzen and Geels also note that mysticism is
...a way of life and a 'direct consciousness of the presence of God' [or] 'the ground of being' or similar expressions.
A mystical experience is an intuitive understanding and realization of the meaning of existence – an intuitive understanding and realization which is intense, integrating, self-authenticating, liberating – i.e., providing a sense of release from ordinary self-awareness – and subsequently determinative – i.e., a primary criterion – for interpreting all other experience whether cognitive, connotative, or affective.