After all that depressing stuff I wrote about websites, let's have a nice picture of an icon. Nowadays we use the word most often in one of its two modern meanings. The OED says:
1a. An image, figure, or representation; a portrait; a picture or illustration in a book
1b. An image in the solid; a monumental figure; a statue.
1c. Computing A small symbolic picture of a physical object on a VDU screen.
2. Eastern Church A representation of some sacred personage, in painting, bas-relief, or mosaic, itself regarded as sacred, and honoured with a relative worship or adoration.
3a. Rhetoric A simile. (Obsolete)
3b. Philosophy A sign which represents its object by virtue of having some character in common with the object.
4. A realistic representation or description in writing. (Now rare or obsolete.)
Oddly, the other modern meaning apart from 1c appears in the OED as a draft addition from 2001, though it was recorded in print fifty years earlier:
A person or thing regarded as a representative symbol, esp. of a culture or movement; a person, institution, etc., considered worthy of admiration or respect. (e.g. "Hollywood's female gay icons Jodie Foster, Susan Sarandon and Jamie Lee Curtis").