This icon represents an open window. It is a large square with four smaller sqaures on each side. The sqaures on the side are one big on the bottom and one smaller one on the bottom to represent shutters.
This Open 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 5,700 icons, all in the same style and quality.