The mandorla or the nimbus is an iconographic symbol in the shape of a circle or an almond-shaped oval signifying heaven, Divine Glory, or Light. Mandorla is Italian for "almond."
The mandorla is one of the clearest and most majestic attributes of Christ in iconography. With it, the glorified body of Christ is depicted beyond the earthly plane of being. Christ's garments are usually bright and worked with gold when shown in this manner. It is also used for the Mother of God in those cases when it has to represent her glory beyond the earthly plane. A mandorla usually consists of three concentric circles most often of different shades of blue pierced by rays of light issuing from subject.
It is found in the icons of Pascha, the Ascension, All Saints, Transfiguration, and the Dormition. The mandorla shows that Jesus is present to the faithful, in these events, from outside time and space. The presence of the mandorla and the rays of light coming from Christ reveal his divinity, something that is beyond human comprehension. The mandorla is simply the iconographic way of representing heavenly glory, mystery, and majesty.