Authorization
In plain terms
Deciding what an authenticated user is allowed to do.
Going deeper
Authorization controls access to resources and actions based on roles or policies, after identity is established. It answers 'now that I know who you are, what can you access?'
Under the hood
Models include RBAC (roles), ABAC (attributes), and ReBAC (relationships); principle of least privilege minimizes blast radius of compromised accounts.
Examples
Admin vs. user permissions, AWS IAM policies, OAuth scopes, file ACLs.
Think of it like...
Like a building keycard that, once you're identified, only opens the floors and rooms your role permits.