A centralized single sign-on (SSO) service for accessing multiple AWS accounts and business applications. It integrates with an external identity provider (SAML/SCIM) and manages permission sets applied consistently across the whole organization.
In SAP-C02 it's the recommended solution for multi-account access for human users, as opposed to creating individual IAM users per account. It integrates natively with AWS Organizations and Control Tower.
AWS IAM Identity Center (formerly AWS SSO) is a concept that can show up on the exam. Check the full guide to see it in context.