When you query an LDAP server (usually but not always Active Directory), you generally query a specific part of its hierarchy.
In Check Point, this is defined as part of the Account Unit (AU).
You may need to query more than one set of servers or a different part of the hierarchy on the same servers.
In either case, you would create a different AU to accommodate.
LDAP Groups are specific to an AU since they refer to a specific part of the hierarchy.
I believe there are examples in the documentation.