This is a Event Accepted 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 12,500 icons, all in the same style and quality.
This icon is a small rectangular calendar. At the top are two spiral bindings and the calendar has a star imprinted in it. At the bottom right of the calendar sits a small circle with a checkmark in the center of it.