Years ago I bought this book by McGrath "Christian Spirituality" and he discusses in the beginning of this volume the word mysticism. I will now quote McGrath-
"1 Mysticism is an approach to the Christian faith which places particular emphasis upon the relational, spiritual, or experiential aspects of the faith, as opposed to the more cognitive or intellectual aspects, which are traditionally assigned to the field of theology. The Protestant reformer John Calvin (1509-64), who is noted for his theological precision, had no difficulty in using the term unio mystica ("mystical union") to refer to the relationship between Christ and the individual believer, but understands this to refer to being united with Christ and sharing in his life and benefits. Some writers therefore contrast "mystical theology" (which deals with the existential or relational aspects of Christian thought) with "dogmatic theology," which focuses on the distinctive ideas of the Christian faith. On the basis of this understanding of the term, a "mystic" or "mystical writer" is a Christian who deals primarily with the experiencing of God and with the transformation of the religious consciousness. In the present study, the term "spiritual writer" is used as equivalent to "mystic" and "spirituality" to refer to "mystical theology" in the specific sense of the terms, noted above.
2 In everyday language, mysticism is an approach to spiritual issues, found in religious and non-religious contexts, which stresses inner experience and corresponding marginalizes or rejects any use of cognitive approaches to spirituality. In this sense of the word, mysticism denotes potentially irrational and anti-intellectual approaches to experience, often regarding apparent contradiction as a virtue. "Mysticism," on this understanding of the word, would mean "concerned with esoteric teaching, enhanced psychological awareness, or exotic sensory experience."
3. Mysticism is used to refer to certain specific schools of Christian spirituality, including the "English mystics" of the fourteenth century (such as Richard Rolle and Walter Hilton) and the "German mystics" of the later Middle Ages (such as Meister Eckhart and Johannes Tauler). Although this usage has become widespread, it is somewhat misleading. First, the writers in question do not use this term to refer to themselves; second, the term implies that their outlook is defined by "mysticism" as defined in sense (2) above, which is often a misrepresentation of their concerns and emphases. Given the widespread use of the term to refer to these medieval schools of spirituality, it is probably impossible to reverse the trend. However, its drawbacks need to be noted and taken into account. . ." pg. 6 Introduction
I recommend one read the article "Mysticism" in the volume "The New Dictionary of Catholic Spirituality" pages 681-692.