The fast view bar is the place where fast views are docked. It may be docked on any side of the workbench.
Here is an example of what a fast view bars looks like:
By default the fast view bar is always visible. You can use the General > Perspectives preference page to hide the fast view bar if it is empty.
These buttons provide a quick way to display the fast views in the current perspective. Fast views are essentially minimized views that have been dragged onto the shortcut bar. Fast views pop up when selected, and revert back to their minimized state when you click outside of the view. They may be oriented either horizontally or vertically according to their configuration. To convert a fast view back into a normal view, click Fast View in the view's menu or drag it back to the workbench. To add a view to the fast view bar you can:
Workbench Window Layout