In Undertale: A term describing a form of death where your SOUL merges back together after being destroyed, thus making it impossible to die whilst fighting Asriel, God of Hyperdeath.
Otherwise: A form of death that strengthens your soul.

A form of death in which one is killed so hard that they loop back around to being alive again.

When you die but come back to life. This is in undertale, a game. Asriel is the god of hyperdeath.