Decapitation

Decapitation is the act of severing one's head from the remainder of its body. This is facilitated as either a deliberate act of murder, or as a method of execution. In nearly all cases, the act of decapitation is fatal for the individual. You can't live without a head. However, there are probably some alien races out there that can regenerate enough tissue that they could conceivably recover from such a severe injury. Robots may also be decapitated, but this does not necessarily yield a termination of their systems.