The name Dark is used to refer to several different concepts in the Kingdom Hearts series:
- The primal force, associated with the heart.
- The realm composed of that force.
- The door between that realm and the Realm of Light.
- The Dark Margin between that realm and the Realm Between.
- The corridors used to move between those realms.
- The Keyblade of that realm.
- The character introduced in Kingdom Hearts Union χ.
- The Portal of Darkness areas within the World of Chaos.
- The area in Hollow Bastion.
- The area in Radiant Garden.
- The Darkside Heartless from Kingdom Hearts.
- The Dark Thorn Heartless from Kingdom Hearts II.
- The Dark Follower Heartless from Kingdom Hearts 358/2 Days.
- The black material type from Kingdom Hearts II.
- The Dark Matter synthesis material from Kingdom Hearts Final Mix.
- The Dark Ring accessory from Kingdom Hearts.
- The Dark Anklet accessory from Kingdom Hearts II.
- The form Roxas's Keyblade takes when equipped with the Hazard Gear.
- The form Riku takes when channeling the power of darkness.
- The ability granted by the Two Become One Keyblade.
- Riku's most powerful ability.
- The magic used by Riku and Terra.
- The element used by Riku and Terra.