People often use the terms tornado and funnel cloud interchangeably. There is however a distinct difference. A condensation funnel is a tornado, not a funnel cloud, if either a) it is in contact with the ground or b) a debris cloud or dust whirl is visible beneath it.
Funnel clouds have no detectable debris or damage at ground level. The same is true for waterspouts. If there is a dark spot appearing on the sea surface underneath a condensation funnel, than it is a waterspout. If not, it's a funnel cloud.
Related features:
Accessory clouds
Doppler radar
