An Organizational Unit (OU) is a container for accounts that enables you to organize your accounts to apply policies according to your business requirements
It's best practice to keep the management account (formerly known as "master account") under the root OU
Root OU
The Root OU is the parent OU for all accounts in an organization and all other OUs in the organization
When you apply a policy to the root OU, it applies to every OU and account in the organization.
