Active Directory Objects
Information in Active Directory are stored as objects.
An object can be uniquely identified by its distinguished name.
CN=Joe,OU=Cabinet,DC=WhiteHouse is the distinguished name for user Joe who is in the Cabinet of White House
CN is the Common Name, or the name used to identify the object. In this case it's Joe
OU is the Orginazational Unit which the object Joe belongs to. In this case its Cabinet.
DC is the Domain Controller of the object. It is often the name of the organization.