Select Float converts a normal selection to a Floating Selection.

Floating selections were used in the first ages of GIMP to perform operations on a limited part of the image. Nowadays, you can do that more easily with layers. This option is persisting. More, a float is automatically created when you move a selection using the move tool without pressing the ALT key (or Shift Alt in Linux). A temporary layer is created in the Layer Dialog. Its name is “Floating Selection”. No more operations can be performed on another layer until the float has been anchored.

Once the wanted operations have been performed on the floating selection, you have to anchor it, that is to say put it in a normal layer, more often the original layer, the last active, by clicking on the anchor button of the Layer Dialog or the “Anchor Layer” option of the Layer menu. You can also put it in a new layer by clicking on the New Layer button of the Layer Dialog.

	Tip
	If you use "Layer Boundary Size", you may have some difficulties in selecting the part of the image you want have in the layer. If you make a rectangular selection and transform it into a float, you can anchor it in a new layer. You only have then to remove the old layer.