Shadow work is a term used in in-depth psychology, spirituality, and personal growth to describe the process of exploring and integrating the unconscious or disowned aspects of the Self.  In-depth psychology explores the concept of the shadow as proposed by Swiss psychiatrist Carl Jung. 

According to Jung, the shadow is comprised of the rejected, forgotten, or disowned parts of our psyche. It encompasses qualities, desires, emotions, and behaviors that we find unacceptable, undesirable, or contrary to our conscious identity. These can be things like our fears, insecurities, or even our more aggressive or selfish tendencies. The shadow is not necessarily negative or evil; it simply contains parts of ourselves that we may have difficulty accepting. It embodies the enigmatic corners of their psyche, where veiled emotions, desires, and thoughts linger, deemed unsuitable or daunting by the ego and the persona.

So, to understand the shadow we need to talk about the ego first.

The ego, as a central aspect of our conscious identity, the I that perceives all that is around us and thinks it is the center of it, often strives to maintain a sense of cohesion, social acceptance, and alignment with our learned, given, chosen values and beliefs. It seeks to present a version of ourselves that is in line with societal norms, family & personal ideals, and moral standards taught in school.