A tenant is a collection of configuration settings shared by all mailboxes associated with the tenant. These settings include:
The auto attendant
The operator extension and/or mailbox
How names are formatted when sent to the PBX over a PBX Link
Custom VeMail settings.
Which profile is used.
Which hospitality server is used to communicate maid and/or MWI status to the PMS (for guest mailboxes only).
Tenants are assigned at the mailbox level, and every mailbox in the system is assigned one, and only one, tenant.