This is a speech bubble in the shape of a rounded rectangle. There is a small curved point sticking out of the bottom of the bubble and coming from the left.
This Comments 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 5,500 icons, all in the same style and quality.