The Clone tool allows you to copy an area of your photo
to another area.
This can be used to remove unwanted items from your photo.
The clone tool is a more general version of the Spot tool.
Unlike other tools, the clone tool is special in that it needs at least one region. However, the regions can not be inverted.
Note: A single Clone tool can have multiple regions. (Each has its own cross-hair cursor.) The advantage of doing this is that they all share the same blend mode, opacity, and color & luminosity selection.