This Calendar 11 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 4,400 icons, all in the same style and quality.
It is the number 11 contained within a rectangle. It appears to be a page from a calendar that is bound at the top. There are two binding rings represented by two small rectangles on the top. The date, which is 11, is written on the page below the binding.