This Plus 1 Day 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 4,600 icons, all in the same style and quality.
The icon is depicting a calendar that is rectangular with sharp edges and a line dividing the top portion from the bottom. In the center of the object is written plus one 'd' indicating plus one day on the calendar.