What is a visible rotating column that does not touch the ground called?

A visible rotating column that does not touch the ground is called a funnel cloud. It forms beneath the base of a rotating thunderstorm when condensed water vapor makes the rising, spinning air visible.

A funnel cloud is not automatically a tornado. A tornado must have a rotating circulation that reaches the ground, usually confirmed by visible dust, debris, or damage. Sometimes the ground-level circulation exists before the condensation funnel visibly connects to it, so meteorologists may classify a storm as tornadic even when a gap remains between the funnel and the surface.

Funnel clouds can occur with supercell thunderstorms, but also with other rotating storms. A dust devil forms from the ground upward in hot, sunny conditions and is not normally attached to a thunderstorm. A waterspout is a tornado that forms over water or a tornado-like vortex over water, while a tornado is defined by its surface-reaching circulation.

The familiar funnel shape is produced by pressure falling inside the vortex, which cools rising air and condenses moisture. The visible cloud therefore shows only part of the circulation; invisible wind can extend beyond it.