Dynamic groups allow you to group Oracle Cloud Infrastructure computer instances as "principal" actors (similar to user groups).
When you create a dynamic group, rather than adding members explicitly to the group, you instead define a set of matching rules to define the group members. For example, a rule could specify that all instances in a particular compartment are members of the dynamic group. The members can change dynamically as instances are launched and terminated in that compartment.
A dynamic group has no permissions until you write at least one policy that gives that dynamic group permission to either the tenancy or a compartment. When writing the policy, you can specify the dynamic group by using either the unique name or the dynamic group's OCID. Per the preceding note, even if you specify the dynamic group name in the policy, IAM internally uses the OCID to determine the dynamic group.