Ghost group means a group without any name.
To create the Ghost group follow the steps:
1. Go to https://www.facebook.com/ and Login to your account.
2. Click the arrow given at the right corner and click "Create Group"
3. In the Group name Copy and Paste "xﱞx".
4. Remove both "X" and click "Create Group" after selecting the members
5. Select the Icon.
6. And you are Done :)