Five separate technologies in Windows Server 2008 R2 now contain the Active Directory moniker in their title. Some of the technologies previously existed as separate products, but they have all come under the global AD umbrella. These technologies are as follows:
. Active Directory Lightweight Directory Services (AD LDS)—AD LDS, previously referred to as Active Directory in Application Mode (ADAM), is a smaller-scale directory service that can be used by applications that require a separate directory. It can be used in situations when a separate directory is needed, but the overhead and cost of setting up a separate AD DS forest is not warranted.
. Active Directory Federation Services (AD FS)—AD FS in Windows Server 2008 R2 is an improvement to the older standalone versions of the ADFS product previously offered by Microsoft. AD FS provides for Single Sign-On technology to allow for a user logon to be passed to multiple web applications within a single session.
. Active Directory Certificate Services (AD CS)—AD CS refers to the latest version of Windows Certificate Services. AD CS provides for the ability to create a Public Key Infrastructure (PKI) environment and assign PKI certificates to AD users and machines. These certificates can be used for encryption of traffic, content, or logon credentials.
. Active Directory Rights Management Services (AD RMS)—AD RMS is the evolution of the older Windows Rights Management Server technology. AD RMS is a service that protects confidential information from data leakage by controlling what can be done to that data. For example, restrictions can be placed on documents, disallowing them from being printed or programmatically accessed (such as by cutting/pasting of content).
Source of Information : Sams - Windows Server 2008 R2 Unleashed