This is the Wstążka zakładka icon for Windows 10. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.
The image appears to be a flag or banner. The basic shape is a rectangle with the long sides standing vertically. At the bottom instead of a straight line to close the rectangle the center point of that line dips up like a triangle is missing from the bottom of the rectangle.