It is a square with a circle inside it. The square has a diagonal line from the bottom-left corner to the top-right corner that splits the square and circle into two triangles with half-circles inside them. The top-left triangle is filled with dots outside of the half-circle, whereas the bottom-right triangle is only filled with dots inside the half-circle.
Related to Invert Selection Icon
Related icons are the icons with matching tags, as well as all editing icons. All icons are in the same flat style. You can either download free PNG icons or buy SVG vectors