A horcrux is an object in which a Dark wizard hides a fragment of their soul in order to become immortal. As long as the object remains intact, so does the soul fragment inside it, keeping the maker anchored to the world of the living, even if their body suffered fatal magic. A horcrux is considered to be the most terrible of all Dark Magic.

Horcruxes can only be created after committing murder, as a means to tear the soul. The process for creating a Horcrux involves a spell and a horrific act was performed soon after the murder has been committed.

Horcruxes are precious to those who made them, so there are usually protective measures to prevent them from being stolen or destroyed, such as counter-charms and curses. Horcruxes are also extremely durable, so only the most powerful and potent elements and magical spells can destroy them, such as Basilisk venom and Fiendfyre.