Well, Now the things are quite clearer than before. I thought that 'domains' were related to Linux also. Anyway.... thanks a lot.

SO I think that the 'Active Directory' services are deployed for the management and configuration of the domains? And the active directory is nothing but the container type object with the elements being the resources for the management of the 'domain'?

Anyway what is the 'Linux equivalent' of the 'Windows Server Domain'?