Idea of Topic Icon
A speech bubble is shaped like a circle, with a small portion (about 1/10) open on the bottom left. Two lines are drawn off of this, that extend a short ways before meeting, to close the bubble. It looks like a circle with a small triangle hanging from it.
This Topic 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 6,100 icons, all in the same style and quality.