This option in the Edit Menu > Select > FLOATING / NOT FLOATING will show you whether or not you have a floating selection active in the design window. 

When you make a selection in your design using any other selections tools (Lasso Tool, Magnetic Lasso Tool, Polygon Tool, Rectangular Selection Tool, Oval Selection Tool or the Magic Wand Tool), that selection is not floating. This means, if you move that selection, the information within the selection will move, leaving behind a space where it used to be. 

If, after creating the selection you go to Edit Menu > Copy (⌘C) and then Edit Menu > Paste (⌘V), this selection becomes a floating selection.  This means, if you move the selection, it leaves behind a copy of the selected area. It remains floating until it is deselected (⌘D).