muqarnas

(Arabic: مقرنص).  A form of decorative vaulting in Islamic architecture. In muqarnas, the surface of a vault or dome is subdivided into niche-like cells that have no load-bearing function. Also know as stalactite vaulting or honeycomb vaulting. Web resource here.

Isfahan_Royal_Mosque_entrance

Muqarnas vault, Royal Mosque, Isfahan, Iran.