Tableau Server is Tableau's server software, which allows you to host reports and dashboards developed with Tableau Desktop, to access them from different computers and devices in your organisation, and to manage security by users and groups. Tableau Server allows you to embed reports into other applications such as Salesforce or Sharepoint.
The purchase of Tableau Server is licensed on a per named user basis, with a minimum of 10 users. It is important to note that to create reports and dashboards you need to use (and license) the Professional version of Tableau Desktop, which can be installed on Windows or OSX computers. You cannot design or create reports directly in a web environment.
Tableau Server Resources