This is a Calendar 30 Filled 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 13,000 icons, all in the same style and quality.
This is a calendar page that is displaying the number thirty. There is no month displayed, nor is there a day. There are, however, what looks like two rings protruding from the top of the page, suggesting that this is a calendar that can be adapted for reuse month after month.