What is Active Directory (AD) ?
Its a new modern service that is based on the REST technology and it provides identity management and access control capabilities for your cloud applications
What is the Function of Azure Active Directory ?
> It easily integrates with your on-premises active directory in order to apply policies and control and authenticate users to their azure credentials and other cloud services.
> It offers access control for the azure application as policy rules are centralized.
> Build Social Connection across the enterprise.
> Provides single sing-on across your cloud applications integrating third party cloud services and applications built on Windows Azure .