Google’s identity service for managing users, groups, and security policies (such as 2-Step Verification) with the company domain, without needing Google Workspace. Identities can be synced from Active Directory with Google Cloud Directory Sync.
On the ACE it comes up when setting up corporate accounts: creating users by hand or automating with GCDS, and granting IAM roles to groups instead of individual users.
Cloud Identity is a concept that can show up on the exam. Check the full guide to see it in context.