This option allows the Administrator to filter the profiles being shown on the Members/Staff sections through various categories available. This is located at the upper right section of the page, right below the search box.
The default screen upon logging in to your account or clicking the Members/Staff icon is No Filter. Clicking the Filter profiles drop-down list, it will show the other filter options applicable for the groups.
When you're viewing the profiles in an eForm (clicking anywhere on the eForm except for the two icons), other filtering categories will be available for you to choose from.