A Jungian concept that refers to dark aspects of ourselves that we don't recognize and haven't accepted or integrated as being some part of ourselves. As we grow and our personalities develop, the shadow develops side-by-side with the ego; it is part of the maturation process. Aspects of ourselves that adults teach us are innappropriate or not to be expressed are disavowed and move from ego to shadow. Shadow is understood as being both personal (pertaining to an individual) and collective (pertaining to a nation or culture). One of its values is that those aspects of ourselves which we have learned to neglect or suppress also make it possible for us to cultivate their opposing strengths and virtues.
Every person's psyche is motivated toward wholeness or integration. This can only happen when shadow aspects of our personality are once again recognized and accepted as equally important parts of all our developmental experiences. In fairy tales this is most often expressed when "ugly" or misshapen characters (guess who?) turn out, in the end, to have been transformed princes or princesses, who can only become their true selves after someone loves them.
Often our first recognition of the shadow, if we are an observant adult, occurs in seeing qualities that we dislike most about ourselves being expressed in someone else. We don't recognize them as an aspect of ourselves, rather our experience is usually one of not being able to tolerate some aspect of that "different" or "difficult" person (see projection).
When shadow aspects are released (expressed alchemically as transforming lead to gold), energy that was used to keep them hidden from the ego often provides or supports a great burst of creative energy.