Hi Tomas,

The territory report lists all territories in your organization. Select No Users in the Users drop-down list and click Run Report to see the territories in your organization that do not have any assigned users.
The User Territory report, User Multiple Territory report, and User Missing Territory report summarize the users who have been assigned to any territories, more than one territory, or no territories, respectively. 
The Account Territory report, Account Multiple Territory report, and Account Missing Territory report summarize the accounts that have been assigned to any territories, more than one territory, or no territories, respectively.
The Opportunity Territory report summarizes the opportunities that are in territories. To see opportunities owned by users who are not currently active in the opportunity's territory, customize the Opportunity Territory report with the following advanced filter: Active in Territory equals “False.” The Opportunity Missing Territory report summarizes the opportunities that are associated with accounts that do not have a territory.
Reports run from custom report types that include territories may display results differently than standard reports that include territories. This is because reports run from custom report types only display results with territories, such as accounts with territories, whereas standard reports that include territories may display results without territories. For example, if you select the Account Territory Report, results display accounts without territories. In custom report types, when using the Territoriesfilter that includes territories, Multiple Territories or Missing Territories are not shown in the report results.

Best Regards
Naga Kiran