This Minimize Window 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.
This is a very simple icon that is composed of a square with slightly rounded corners. Inside the square is a thin rectangle with rounded corners. It is placed near the bottom of the larger square to represent the handle of a window.