This is the number twenty drawn inside of a square. The square has a line near the top, separating about 1/4 of the square. The top of the square has two little tabs.
This Calendar 20 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.