This page contains the About vector icon, as well as variations of this icon in different visual styles, and related icons. All icons are in the flat vector style, however, differ by the line thickness, fill, and corner radius.
It is a speech bubble with the letter "i" in the center. The bubble is not an exact circle, but rather a horizontal oval. The letter "i" is lower case, and one would think that by seeing this icon you would be informed about a certain topic presented with it.