This Navigation Toolbar Bottom 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 4,900 icons, all in the same style and quality.
The icon is shaped like a rectangle with round edges. About a third of the way down there is a horizontal line running through it. In between the horizontal line and the base of the rectangle are two small circles followed by a long skinny rectangle.