APA Dictionary of Psychology

a defensive reaction involving withdrawal into inactivity, detachment, or fantasy as an unconscious defense against anxiety-provoking situations. This may be expressed as a number of defensive behaviors, such as rationalization, daydreaming, or substance abuse. It may include a retreat into psychotic behavior as a means of avoiding real or imagined problems. Also called retreat from reality. See also escape from reality. Compare flight into fantasy; flight into reality.