The Selection Filter is available during most Edit functions. If you are working with a dense design, the selection filter helps you filter out the items that you do not want to select. It also allows you to select multiple items and items on specific layers.
When you are not in a command that uses the Selection Filter, the text in the Selection Filter is gray and you cannot select any options. You also do not have the option of using the View|Selection Filter command or the F hotkey when not in a function that uses the Selection Filter.
You can close the display at any time by clicking on the X in the upper-right corner. If you undock the Selection Filter from the VisualCAM window while not in a function that uses it, it will disappear. It will automatically appear again when a function requires it.