The Flip tool provides the ability to flip layers or selections either horizontally or vertically.
When flipping selections, a new layer will be created and the old layer that the selection was created on will have that area "cut" from it.
Flip Tool Settings
The Tool Toggle settings control flipping in either a Horizontal direction or a Vertical one. This toggle can also be switched using a key modification.
Default Keyboard Shortcut: Shift-F
Ctrl toggles the flip direction.