Karl, who had his leg amputated after an injury, reports that he still feels pain in his missing leg. such an experience is referred to as pain.

The answer to this question would be phantom pain 

An amputated leg sometimes still giving a fell of leg or pain even though the leg wasn't there anymore. That happened because the nerve fiber that carries the stimulus from that area is still alive. Something might induce the remnant of the nerve to send a signal of pain but the brain interprets the location to be in the removed limb.