This icon is a small circle with another circle behind it. The first circle has the number "1" in the center of it. You cannot see the circle behind the first circle. It looks like it could be a 3D cylinder.
This Average icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,700 icons, all in the same style and quality.