What is Forest , Tree and Domain in Active Directory

Forest :
Forest is the highest level of organization within Active Directory. The trees in the forest are also under transitive trust relationship with each other. A forest does not require a specific name.

Tree :

A Tree in Active Directory is the collection of domains
The term refers to the fact that each domain has exactly one parent and in the forest trust each other, meaning the user of any specific domain of that forest can have access to all other resources in that same forest in which they are working.

[chiang_tzu_hsien]

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[memedaddyz]

Tree is a collection of AD domains that begins with a single root domain.