The Kind section of the Find window contains two pop-ups that can be used in tandem to limit searches to specific kinds of items. If neither option is checked or this section is hidden, then all types of items can be found in searches.
Item kind
Use the left pop-up to specify a general class of item for which you wish to search. The options are:
Kind subclasses
Use the right pop-up to limit searches to specific subclasses of the kind currently shown in the left pop-up. The contents of this pop-up menu will change depending the current item in the item kind pop-up on the left.