Muqarnas, also known in Iberian architecture as Mocárabe, is a form of three-dimensional decoration in Islamic architecture in which rows or tiers of niche-like elements are projected over others below. It is an archetypal form of Islamic architecture, integral to the vernacular of Islamic buildings, and typically featured in domes and vaults, as well as iwans, entrance portals, or other niches. It is sometimes referred to as "honeycomb vaulting" or "stalactite vaulting".
Muqarnas as seen from below in the iwan entrance to the Shah Mosque in Isfahan, Iran (17th century)