It is a type of icon found in both Greek and Russian iconography, one of the major church festivals.

The type depicts the descent of the Holy Spirit upon the Apostles on the Day of Pentecost, as described in the second chapter of Acts. At the top of this image is a descending flame — the fire of the Holy Spirit.  Some examples show individual tongues of flame resting on the heads of the Apostles.  The icon takes some liberty, however, in placing the later apostle Paul across from the apostle Peter at the top of the group; Paul was not present at the “descent,” but was added in iconographic convention nonetheless. Also Mary is included at the head of the Apostles in the above example, though she is omitted in many others, leaving the chief seat empty — the situation of the Apostles after Jesus ascended and before the Holy Ghost descended upon them as their comforter and teacher. In Greek icons, the four Evangelists may be anachronistically included, and the youngest apostles are often placed in the two lowest seats.