Muqarnas are a form of architectural ornamented vaulting, the "geometric subdivision of a squinch, or cupola, or corbel, into a large number of miniature squinches, producing a sort of cellular structure", sometimes also called "honeycomb" vaults from their resemblance to these. They are used for domes, and especially half-domes in entrances and apses, mostly in traditional Islamic and Persian architecture. When some elements project downwards, the style may be called mocárabe; these are reminiscent of stalactites, and may be called "stalactite vaults". See: https://en.wikipedia.org/wiki/Muqarnas