Quantum suicide refers to a thought experiment that uses a variation of the Schrödinger's cat experiment to distinguish between two types of quantum mechanics interpretation: the Copenhagen and the Everett many-worlds interpretation. Quantum immortality refers to the experience of surviving one's own quantum suicide.
In the Copenhagen interpretation, the wave function eventually collapses, which means that a state wherein the subject is dead has already happened. However, in the Everett many-worlds interpretation, every possible outcome is accommodated by a copy of the world in which a specific outcome occurs. Therefore, a subject assumes a superposition whereby it is impossible for him to experience his own death because there is always a copy of the world in which he survives.