In AWS IAM Roles are similar to IAM Users in that they can have policies and permissions attached to them. However, they cannot be authorized (login) and they do not really have the policies etc attached to them. They appear to have them but underneath, those policies flow down the the actual users beneath.
The idea is that Roles will help you to group users together and also that they can help you in temporarily granting a level of access or permission to a user and give you an easy way to revoke that.
