AD LDS is Active Directory Lightweight Directory Services and was previously known as ADAM (Active Directory Application Mode).
This is a role first made available in Windows Server 2008. ADLDS is a LDAP server. See http://go.microsoft.com/fwlink/?LinkId=96084 for an overview.
The following step by step guide should be useful to anyone new to ADLDS http://technet.microsoft.com/en-us/library/cc731246(v=WS.10).aspx .