A compass with a lid that covers and protects the crystal. One of the best known examples are the WWI pocket watch compasses also referred to as Hunter cased (after the pocket watch design). In a closed face compass the lid can be hinged or lift off completely. In either case the lid totally protects the compass crystal when closed.
The lid can be fitted with a viewing window, and this feature is quite common on military type compasses.
The use of a viewing window ensures that a bearing can be checked, eliminating the need to open the compass.