Visibility defines if other people can see your collection or not. There is 3 level of visibility, from the least restrictive to the most:

1. public -> everyone can see your collection
2. internal -> only logged in users can see your collection
3. private -> no one but you can see your collection

Visibility can be set on each item individually.

You can also set visibility globally in the settings page.

1. If set to private -> nothing from your collection is visible, regardless of an item own visibility
2. If set to internal -> only items with public or internal visibility will be share with logged in users
3. If set to public -> public items will be visible to anyone, public or internal for logged in users