He's after you Mr. Potter. I'm afraid you really don't stand a chance. I suppose I'll have to kill him before he finds me then.
Daniel Radcliffe: They all know, that the reason they're on this journey, to destroy Horcruxes and Voldemort, is much bigger than any one of their individual lives. They need to destroy Voldemort, in order to save the Wizarding World. They know that the Horcruxes are the key.
Harry Potter and the Deathly Hallows Part 2: Horcruxes
The Horcrux is an object which a person has concealed out of their soul.
David Barron: Voldemort is terrified of dying. And he's got this incredible lens, to make sure that he stays immortal. Emma Watson: Voldemort has split his soul into seven pieces. And he has hidden these seven pieces of his soul in different objects that are related to his past and are related to him and who he is. Harry has already destroyed the diary, Tom Riddle's diary had a piece of his soul in it. Dumbledore destroyed the ring, so that's two. The locket, that one's destroyed. So they got four Horcruxes to find and destroy.