Different from windows Active Directory

web based auth standards: OpenID and OAuth based

A tenant is a dedicated, isolated instance of the Azure Active Directory service, owned and managed by an organization.

Tenants can be owned by individuals, teams, companies, or any other group of people. Tenants are commonly associated with companies.

If you sign up for Azure with an email address that's not associated with an existing tenant, the sign-up process will walk you through creating a tenant, owned entirely by you.

Azure AD tenants and subscriptions have a many-to-one trust relationship: A tenant can be associated with multiple Azure subscriptions, but every subscription is associated with only one tenant.

This structure allows organizations to manage multiple subscriptions and set security rules across all the resources contained within them.