The formations that hang from the ceiling of a cavern like icicles are called stalactites.

Here's the difference between stalactites and stalagmites:

* Stalactites: Hang from the ceiling like icicles and are formed by dripping water.

* Stalagmites: Rise from the floor of the cave and are formed by the water that drips from stalactites.

Both are created over long periods of time through a process called cave dripstone formation.