Meaning & CommunicationRevised
Icon
A form that represents a concept by resembling it directly, as opposed to a Symbol, which represents by convention.
In practice
In this dictionary, an icon is a sign that works by resemblance: it looks like what it means. A small drawing of a trash can meaning delete, or an envelope meaning mail, is an icon in this sense. Many interface symbols called icons are in fact conventional, like the floppy disk for save, which many users have never seen in real life, so it now works by habit rather than resemblance.
Often confused with Symbol
An icon means something by looking like it; a symbol means something only by learned agreement, like a heart for love.
Try this
Draw five interface icons from memory and sort them into ones that resemble their meaning and ones that work by habit.