The AWS service for managing identities (users, groups, roles) and their access permissions to AWS resources. It follows the least-privilege principle. Permissions are defined in JSON policies.
Fundamental for CLF-C02 and SAA-C03. Key concepts: an IAM user (a permanent identity), an IAM role (a temporary identity assumed by services or users), a policy (a JSON permissions document). Question: what do you assign to an EC2 instance so it can access S3? An IAM role, never user credentials.
IAM (Identity and Access Management) is a concept that can show up on the exam. Check the full guide to see it in context.