The shadow, as Carl Jung conceived it, is the totality of everything in the psyche that the conscious personality has rejected, repressed, or refused to identify with. It is not simply the "bad" parts of the self — though those are there. It is everything that was deemed unacceptable, dangerous, embarrassing, or incompatible with the persona (the face we show the world): the anger that was not allowed, the neediness that was shamed, the ambition that was called selfish, the sexuality that was called sinful, the grief that was told to stop. But the shadow also contains gold — gifts, capacities, and strengths that were suppressed for the same reason, because they were somehow threatening to the self-image or to the people whose approval was needed.
Jung described the shadow as the "dark side of the personality" — not in a moralistic sense but in the literal sense of what lives in the dark, outside the light of conscious awareness. Everything that cannot be acknowledged by the ego gets pushed into the shadow, where it continues to operate outside conscious control. This is why people are often blind to their own most obvious qualities — the arrogance of someone who claims only to be confident, the contempt of someone who claims only to have high standards, the terror of someone who insists they are only "being practical." These disowned qualities are operating from the shadow, influencing behaviour without the person's awareness or consent.
The shadow is not a Jungian invention — it is a structural feature of the human psyche. Every tradition that has engaged seriously with human psychology has encountered it: the Buddhist concept of the "hungry ghost" who drives compulsive behaviour; the Christian doctrine of sin as a power that operates against the conscious will ("the good that I would I do not; and the evil that I would not, that I do" — Paul, Romans 7:19); the Sufi understanding of the nafs (the lower self) as the source of self-deception and automatic reactivity. Jung gave it a name and a systematic framework, but the reality it describes is universal.