Fast views are hidden views that can be quickly opened and closed. They work like other views except they do not take up space in your Workbench window. 

Fast views are represented by toolbar buttons on the fast view bar, which is the horizontal toolbar on the bottom left of the Workbench window. When you click the toolbar button for a fast view, that view opens temporarily in the current perspective. As soon as you click outside that view, it is hidden again.

You can create a new fast view by dragging any open view to the shortcut bar or by selecting Fast View from the menu that opens when you click the icon at the left end of the view's title bar.

Workbench
Toolbars

Creating fast views
Moving and docking views
Maximizing a view or editor