Phantom pain, also called deafferentation pain, anesthesia dolorosa, or denervation pain, is pain that is felt in a part of the body (usually an extremity) that either no longer exists due to amputation or is insensate as a result of nerve severance. It is often described as a burning sensation, though individual accounts vary. This pain does not originate from the limb itself, as such would be impossible in these cases, but is instead the result of the brain receiving messages from the spinal cord which it interprets as pain coming from the affected limb. 
Pain usually begins when nerve endings relay information to nerves, which in turn relay it to ganglia just outside the spinal vertebrae, which send it to nociceptive (pain-sensing) neurons inside the spinal cord, which finally send the information to the brain. If the nociceptive neurons cease to receive information to pass on, they will instead send the neurological equivalent of white noise, which the brain then interprets as pain. 
In cases in which a traumatic event causes nerve severance and also detaches the nociceptive neurons from the rest of the spinal cord, phantom pain will not develop. Some patients who do not receive adequate relief from nerve blocks, narcotic painkillers, or other methods of pain management may undergo a procedure called dorsal root entry zone (DREZ) lesioning. DREZ lesioning is a form of neurosurgery in which the wayward nociceptive neurons are destroyed.