It's a logo of a calendar page with two rings on top and then the page hanging down from them. There is a line across the top of the page and in the lower bigger section is the number "23".
This Calendar 23 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.