This filter will be replaced by the new filter framework soon.
With this menu you can filter the caches shown on the live map, nearby list, and when searching by type. Just select the cache type.
The filter setting will remain active (even if you restart c:geo) until you change or reset it.
Please note that you can currently either see all caches or only filter exactly one type of cache.
The different cache types are explained in the section Geocache Type Icons in c:geo.