In computing, an organizational unit (OU) provides a way of classifying objects located in directories, or names in a digital certificate hierarchy, typically used either to differentiate between objects with the same name (John Doe in OU "marketing" versus John Doe in OU "customer service"), or to parcel out authority to create and manage objects (for example: to give rights for user-creation to local technicians instead of having to manage all accounts from a single central group).
They might represent geographical regions, job-functions, associations with other (external) groups, or the technology used in relation to the objects.
Examples would include: In Sun Java System Directory Server and Microsoft Active Directory (AD), an organizational unit (OU) can contain any other unit, including other OUs, users, groups, and computers.
OUs let an administrator group computers and users so as to apply a common policy to them.
Organizational Units give a hierarchical structure, and when properly designed can ease administration.