OOC- have you read Harry potter and the half-blood prince?
heres the definition from wikipedia
In the Harry Potter universe, a Horcrux is a magical object created through the use of the Dark Arts. It is defined as a "receptacle in which a Dark wizard has hidden a fragment of his soul for the purposes of attaining immortality."[1] With part of a wizard's soul thus stored, the wizard becomes immortal while the Horcrux remains active, hidden away in a safe location. If the wizard's body is later destroyed, the remaining part of the soul remains preserved within the Horcrux.[2] However, the destruction of the Horcrux creator's body leaves the wizard in a state of half-life, "lesser than the meanest ghost."[3]. Lord Voldemort was left in this state when his attempted use of a Killing Curse on Harry Potter backfired upon himself.[4]
A Horcrux can be made from any normal object: Lord Voldemort used a diary, a ring, and other objects as Horcruxes. Horcruxes may be concealed for security, but if discovered are vulnerable to destruction, as is seen with Tom Riddle's diary and Marvolo Gaunt's ring.[5] Destruction of the Horcrux destroys the fragment of soul contained within it, ending the protection it provides, and rendering the creator mortal, assuming s/he has no remaining Horcruxes. A human must have at least one piece of his soul intact on Earth in order to continue living, so if all of the Horcruxes of a person had been destroyed, then there would be no way for them to return after being killed, because killing them would remove the last piece of their soul remaining, that inside their body, from mortal existence.[6] It is unknown what happens if a person with Horcruxes is kissed by a dementor.
Even though Albus Dumbledore confirmed that others have created a Horcrux before, Lord Voldemort is the only wizard explicitly mentioned as having created a Horcrux, and he is the only wizard known to have created more than one, thus going "further than anybody along the path that leads to immortality."[7]