Invert SelectionΒΆ
Inverts the current selection.
Vertex - 
Edge - 
Polygon/UV Island - 
When you go to
Invert Toolwith the polygons selected like the left image, the result will become like the right image.
Inverts the current selection.
Vertex -
Edge -
Polygon/UV Island -
When you go to Invert Tool with the polygons selected like the left image, the result will become like the right image.