There is a square calendar box with a header and two pins at the top. Inside the square is an uppercase S and lowercase u, for Sunday.
This Sunday 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.