The first is the parent domain, and everything after that is a child domain. So you might have something like.
parent.local this would be the first domain of the parent domain
child.parent.local is the second or child domain
The forest root domain.
Forest
Active Directory
In Windows Server 2011 it is called Active Directory.
domain name service
no
*Schema NC, *Configuration NC, * Domain NC Schema NC This NC is replicated to every other domain controller in the forest. It contains information about the Active Directory schema, which in turn defines the different object classes and attributes within Active Directory. Configuration NC Also replicated to every other DC in the forest, this NC contains forest-wide configuration information pertaining to the physical layout of Active Directory, as well as information about display specifiers and forest-wide Active Directory quotas. Domain NC This NC is replicated to every other DC within a single Active Directory domain. This is the NC that contains the most commonly-accessed Active Directory data: the actual users, groups, computers, and other objects that reside within a particular Active Directory domain
Active Directory was previewed in 1999, released first with Windows 2000 Server edition, and revised to extend functionality and improve administration in Windows Server 2003. Additional improvements were made in Windows Server 2003 R2. Active Directory was refined further in Windows Server 2008 and Windows Server 2008 R2 and was renamed Active Directory Domain Services. Active Directory was called NTDS (NT Directory Service) in older Microsoft documents. This name can still be seen in some Active Directory binaries.
Security Identifier (SID) and Domain Name (DN) (p. 86)
Security Identifier (SID) and Domain Name (DN) (p. 86)
the Domain is called as the security boundary with in the active directory. A Windows domain is a logical group of computers running versions of the Microsoft Windows operating system that share a central directory database. domain governs the way user access resources of the network
Name the AD NCs and replication issues for each NC*Schema NC, *Configuration NC, * Domain NCSchema NC This NC is replicated to every other domain controller in the forest. It contains information about the Active Directory schema, which in turn defines the different object classes and attributes within Active Directory.Configuration NC Also replicated to every other DC in the forest, this NC contains forest-wide configuration information pertaining to the physical layout of Active Directory, as well as information about display specifiers and forest-wide Active Directory quotas.Domain NC This NC is replicated to every other DC within a single Active Directory domain. This is the NC that contains the most commonly-accessed Active Directory data: the actual users, groups, computers, and other objects that reside within a particular Active Directory domain.
Yes it is possible that a forest has one or more domains which have trusts between them
Forest Root Domain