It is the practice by which we become more intimately involved with God and with the spiritual world in a sanctified way. The phrase “Christian Mysticism” distinguishes this from unprotected contact with the spiritual realm such as you might find in some popular New Age or occult practices like tarot card reading or “channeling”, which are prohibited for faithful Christians.
The Rosary, for example, is a form of meditation that takes about the same amount of time on a daily basis as other kinds of meditation, since as I remember from my college days the goal of many students in the guru movement was to meditate about 20 minutes daily. That is about the amount of time it takes to say five decades of the Rosary.
So, what is the difference? The difference is that you begin the Rosary by first addressing God through the sign of the cross and secondly by repeating prayers taken straight out of Scripture and blessed by God through Mary for our use. This is a form of protection that sets us apart from destructive spirits while we grow in the mystic realm in which we can grow to perceive God in a way that we cannot explain, rationally. (thus the term, “mystic”)
Just about every religious Order includes many prayers that focus the mind and soul on God to a lesser or greater extent depending on the life duties of the members. The lesser associations such as Third Orders of laity, confraternities, and lay associations may use the Rosary only several times a week as a mystic devotion or may use daily prayer plus a variety of special practices to increase the special holiness of life of the members. There are also practices such as the exercises of Ignatius Loyola and the writings of the Carmelite saints that lead people through stages of spiritual growth in the mystic sense.