Many tools have views which display information of some sort in the form of a list. Items in these lists may be selected, and you can usually perform operations on selected items (for instance, by means of the standard action commands, as described in Performing operations on selected objects).
Such lists are often very long, and there may be information displayed which you are not interested in. For instance, Common Lisp objects may contain a large number of slots, most of which are of no importance to your work.
Most such lists in Common LispWorks have a filter area which lets you hide redundant information. The filter area is above the list, and consists of the Filter pane into which you can enter text, toolbar buttons, and the Matches pane. There is also a filter modes dropdown menu, described in Advanced Filtering.