An icon, as it relates to geocaching, is an image available on a geocacher's statistics page (notably on Geocaching.com. Different icons represent differing kinds of caches and/or hitchhikers that a given cacher has found, hidden, or released.
On the Geocaching.com website, there are different icons for traditional caches, multi-caches, virtual caches, puzzle/mystery caches, webcam caches, locationless (reverse) caches, event caches, and recently mega-event caches. Special icons exist for the Project APE series, for EarthCaches, and for CITO events. Benchmarks, put out by the National Geodetic Survey, also have an associated icon.
Hitchhikers also have their own icons as well. Travel Bugs have a generic icon. The primary exceptions are travel bugs released by Jeep as part of their geocaching promotion, whose icons are associated with Jeep travel bugs released in different years. Geocoins have their own icons. Originally, a generic icon was associated with all geocoins trackable through Geocaching.com, but with the advent of state geocoins and other geocoin types, each specific type of geocoin has its own icon.