Privacy Settings is a field on both the Account and Contact records. Privacy Settings affect the ability of portal users to search for Accounts and Contacts when registering for Lightning Events.
Privacy Settings for Accounts:
Privacy Settings for Contacts:
Public allows any user in the system to search for the Account or Contact.
Private allows the Account or Contact to be searchable by authenticated users only.
Unlisted Accounts and Contacts will not appear in any search result.