A stalactite is a formation found hanging from the ceilings of caves. Another similar formation can be found on floors of caves and are called stalagmites.
Confusion about which is which can be avoided via the following simple mnemonic: Tites go down and mites go up.
Can also be remembered by 'tites stick tight to the ceiling, 'mites might reach the top.
Or by remembering stalactites have a 'c' for ceiling, so they are stuck to the ceiling; and stalagmites a 'g' for ground, so they grow up from the ground.