You can now reference Organizational Units (OUs), which are groups of AWS accounts in AWS Organizations, in AWS Identity and Access Management (IAM) policies, making it easier to define access for your IAM principals (users and roles) to the AWS resources in your organization. AWS Organizations lets you organize your accounts into OUs to align them with their business or security purpose.  

from Recent Announcements: https://aws.amazon.com/about-aws/whats-new/2019/11/use-iam-share-aws-resources-with-groups-aws-accounts-aws-organizations/