What is an icon?

In the Broadest Sense

Typically when someone refers to an icon it will refer to a picture or a representation of some kind. Meanings behind icons are usually highly figurative.

In computers

An icon is a image or a small picture that may let you open a file. You will often find these icons on the desktop of your computer.

Usually desktop icons will represent something about the application you are opening. For example, the "Recycle Bin" icon is a trash can, meaning you are going to throw away a file. Another example is the Itunes icon. It is a CD with a musical note on it, representing music and other entertainment media that can be bought and played.

In people

An icon can be a person famous, usually for something in particular. For example, Elvis could be seen as an icon of rock and roll music and Michael Jackson can be seen as an icon of pop music.

Nowadays you will hear the term "gay icon." This is a person that represents or advocates the gay community. Examples of gay icons include Cher and Madonna.

In religion

Found prevalently in the Orthodox and Catholic Churches an icon is a representation of some religious figure. Often times in the latter churches it is of Mary or Jesus. For example, the icon "Theotokos of Vladimir" clearly represents Mary and Jesus though the name literally means "Virgin of Vladimir." Often times people will add their own culture to paintings, meaning they will change names to reflect their own cultural names and they will also change the likeness of figures to represent what they themselves look like all the while they keep the same figurative meaning.