An IAM Role in AWS is an identity that you can create within your AWS account that has specific permissions. It's different from a user in that it doesn't have any credentials stored, but rather relies on the underlying trust relationship between the identity provider and AWS. When an IAM Role is assumed, the underlying security credentials are generated dynamically and provided to the application or service assuming the role. This allows for greater flexibility when granting access to resources as well as allowing for fine-grained control of which services are allowed to assume which roles. Additionally, it enables applications and services to easily rotate their access credentials without needing manual intervention.