There are three visibility modes your collection can be in: public, unlisted and private.
Public means that your collection can be viewed by anyone, found in search engines and seen on your profile.
Unlisted means that only people who have the link can see it, so it won't appear in search or on your profile but you can give the link to people.
Private means that only you can see the collection, while logged in.
To change the visibility of your collection:
- Click the Lock, Eye or Globe icon on the right of your collection's name
- In the popup that appears, choose Public, Private or Unlisted.
- Click Save.
See here for more: