Muqarnas is a form of architectural ornament built from many small nested, tiered niche-like cells, corbelled outward and stacked so that each tier oversails the one below it, used to decorate and structurally soften the transition between a flat wall or squinch and a dome, vault, or projecting cornice above it. Unlike flat surface decoration such as tilework or carved stucco, muqarnas is fully three-dimensional, catching real light and shadow across its many small concave and convex facets so that its appearance shifts through the day as the sun moves; the effect has often been compared to stalactites, though the resemblance is coincidental rather than the origin of the form.
Muqarnas can be built in stone, brick, carved and painted wood, or molded plaster and stucco, and the technique allowed builders to render extremely complex geometric transitions, portal hoods, domed ceilings, and the underside of arches, in a unified sculptural surface rather than a series of separate flat panels. Because assembling a muqarnas vault correctly requires solving the geometry of dozens or hundreds of individually shaped cells so that they fit together into a coherent overall dome or niche form, muqarnas design became a specialized craft with its own body of geometric knowledge passed between master builders.