This is a Calendar 25 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 12,600 icons, all in the same style and quality.
This icon is depicting a calendar with a number 25 on it. The object is rectangular shaped with a solid horizontal line dividing the topmost part from the bottom. In the center of the calendar is the number 25.