Phantom voltage
An inconsequential voltage many testers will detect. It may register as a lower or a full voltage found on a wire that is connected neither to hot nor to neutral/ground. It seems to come about by means of capacitance or inductance from a hot wire that is near the unconnected wire over a good distance in the same cable. See this explanation. ...Do not confuse phantom voltage with "phantom load," which is the consumption of electricity by a TV when it is plugged in but not turned on, or a charger when it is plugged in but not charging anything.