Sara Soueidan:
An icon button is an icon that triggers some sort of action on the page. More accurately, technically speaking, an icon button is a button that contains an icon and no (visible) accompanying text.
Putting aside the UX side of the coin and whether or not an icon alone is enough to convey meaning and functionality to users, many implementations of these buttons today lack the proper accessibility that makes them meaningful to users of assistive technologies.
Sara gives us 5 techniques to solving this.