1.  Most versions of magical theory consider dreaming to be a form of awareness of the astral realm, and deliberate control of dreams has been practiced by a variety of different magical traditions as a way of astral travel.

The study and interpretation of dreams is also a very old and widely practiced form of divination. Handbooks of dream interpretation have been available since ancient Greek times, if not before; most of them, like their modern equivalents, give long lists of objects or persons, along with the meaning of each if it appears in a dream. The focus on dreams in modern psychology is thus only a recent form of a very old (and generally occult) tradition.

2.  Stories experienced during sleep. Some dreams seem merely to be translations of physical experiences, others seem to be ways we assimilate new information. Dreams are also a function of the subconscious mind and deliberate dreaming is a doorway into the subconscious and its connection to the Collective Unconscious.

See also: Door Without a Key