Active Directory is a database which stores the data like the user information, computer information and also other network object info. It has the capabilities to manage and administer the complete Network which connect with AD.
A relative distinguished name (RDN) is the name used to uniquely reference an object within its parent container in the directory.
A forest is a collection of one or more domain trees. These domain trees share a common Configuration container and Schema,and the whole trees are connected together through transitive trusts.
Forests are named after the first domain that is created when creating a new forest, also known as the forest root domain.
Lightweight Directory Access Protocol LDAP is the industry standard directory access protocol, making Active Directory widely accessible to management and query applications. Active Directory supports LDAPv3 and LDAPv2.
The Global Catalog is a catalog of all objects in a forest which contains a subset of attributes for each object. The GC can be accessed via LDAP over port 3268. The global catalog is read-only and cannot be updated directly.The Global Catalog (GC) is a very important part of Active Directory because it is used to perform forest-wide searches.