It's a logo of a calendar page with two rings on top and the page hanging down from them. There's a line across the top of the page and then in the lower bigger section is the number "4".
This is a Calendar 4 icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,700 icons, all in the same style and quality.