ambulatory (byz. arch.)
A continuous passage that envelops the naos or the centrally planned core of a structure. In a cross-domed church, where the dome is supported on four masonry piers and between each pair of piers two columns are inserted, the ambulatory is formed by the lateral aisles and western part of the church. Later on, an ambulatory could also envelop a cross-in-square core. During the Palaeologan period, ambulatories, usually serving as funerary chambers, were added to many middle-Byzantine churches of Constantinople.

apse
An arched srtucture or a semi-circular end of a wall. In byzantine architecture it means the semicircular, usually barrel-vaulted, niche at the east end of a basilica. The side aisles of a basilica may also end in an apse, but it is always in the central apse where the altar is placed. It was separated from the main church by a barrier, the templon, or the iconostasis. Its ground plan on the external side could be semicircular, rectangular or polygonal.

atrium
1. Antiquity: The large, open space within a building, which is envelopped by colonnades.2. Βyzantium: The forecourt of a church in early Christian, Byzantine, and medieval arcitecture. It was usually surrounded by four porticoes (quadriporticus).

cross-domed basilica
Type of domed basilica. A church plan, whose core, enveloped on three sides by aisles and galleries with a transept, forms a cross. The core is surmounted by a dome in the centre.

cross-in-square church
Type of church in which four barrel-vaulted bays form a greek cross; the central square of their intersection is domed. The cross is inscribed into the square ground plan by means of four corner bays.

dome
A characteristic element of Byzantine architecture. The dome is a hemispherical vault on a circular wall (drum) usually pierced by windows. The domed church emerges in the Early Byzantine years and its various types gradually prevail, while they are expanded in the Balkans and in Russia.

katholikon
The main church in a monastic complex, heart of the monastic activity.

marble revetment
Τhe facing of a wall with slabs of marble

orans
(lat., mean. praying): An iconographic type which was used mainly for representations of the Virgin in Byzantine art. It depicts a standing, frontal figure with its hands open, lifted to shoulder height to either side.. It was the typical early Christian posture of praying, byt in Middle Byzantine years, when the prayer is depicted with the proskynesis type, the orans type becomes more rare.

Tree of Jesse
A metaphorical image that was developed in the West and is introduced, from the 13th c. on, in Byzantine painting as well. Inspired from Isaiah (11,1), it depicts the descent of Christ from the biblical king David through his mother, Maria. Jesse, David's father, is the root of the tree (hence the image's name). The theme was used by both Serbian and Byzantine dynasties as visual means for justifying their imperial claims.