Wikipedia: Icon

An icon (also spelled "ikon", from the Greek word ikon "image") is an artistic representations or symbol? of anything considered holy and divine, such as paintings (including relief? paintings), sculpture, or mosaics, sometimes quite small in size, generally regarded by their users as a physical manifestations of the thing represented. Icons are used particularly in Eastern Orthodox churches and places of worship. In such use, they are typically paintings on a piece of wood. Many religious homes in Russia, for example, have icons hanging on the wall. There is a rich history and rich patterns of [religious symbolism]? associated with icons. The Orthodox sometimes call them "windows into heaven".

In practice, icons are often illuminated with a candle or jar of oil with a wick. Besides the practical purpose of making them visible in an otherwise dark church in the days before electricity, this symbolically means that the saint(s) depicted are illuminated by the Christ, the Light of the World. Orthodox Christians venerate or show honor and respect for icons in a variety of ways, in order to show honor and respect for the people and events depicted. They do not worship icons, for worship of icons was forbidden by the same council that defended their use, the Second Council of Nicaea (also known as the Seventh Ecumenical Council). By venerating icons, Orthodox Christians acknowledge that matter is not inherently evil, but can be used by God. St. [John of Damascus]? observed that iconoclasts who attacked the use of icons often found themselves denying the goodness of matter to such an extent, that they wound up doubting the real incarnation of Jesus Christ as fully human, or that he was resurrected with a real physical body.