Organizational Units
An Organizational Unit (OU) is a logical object in AD DS for collecting users, groups, and computers. You can use OUs to consolidate users, computers, groups, and other objects for simplified management using GPOs linking, or to delegate administrative rights. You can also use OUs to represent a hierarchical and logical structure inside the organization domain. Although no specific rule exists for a logical OU structure, you can create OUs to represent departments in an organization, geographical regions, or anything else based on your organization needs.
If you want to organize the hierarchical and logical structure of your organization, it isn't recommended to add more than five levels of OUs nesting. Although there's no limit for the nesting of OUs, the Distinguished Names can become very long, which could cause problems for some applications.