With Moodle 3.3, you can make links to activities/resources which do not show on the topic homepage. Previously you may have created an orphaned module (ie not showing in the topic homepage) and linked to the activities/resources in that module from other (viewable) modules. With 'stealth', you can now make these Available but not shown on topic page. This feature means you can put activities/resources in the module where they belong, viewable to staff (with a topic coordinator/teacher role) but not to students.
Watch this 2.44 min video explaining stealth activities:
Turn editing on in your topic
For the activity/resource you want to stealth, in the pull-down menu for Actions select 'Hide'
The activity/resource will now say 'Hidden from students'
For the same activity/resource, return to the pull-down menu for Actions. You will now see the option select 'Make available'
Select this option. The activity/resource will now say 'Available but not shown on topic page'. When a student visits the page, they will not see the activity/resource but if you provide a link to it, they will be able to access it