What type of Active Directory structure is a collection of related domain trees called?

A collection of related domain trees in Active Directory is referred to as a Forest. A Forest serves as the top-level container in the Active Directory hierarchy and encompasses multiple domain trees that share a common schema and global catalog.

Each domain tree within a Forest can be seen as a collection of domains that are interconnected, often with a parent-child relationship. This arrangement allows for a structured and organized way to manage security and resource permissions across the entire collection of domains. A Forest can contain one or more domain trees, and because they use a single schema, they can easily communicate and share resources.

The other options serve different purposes within Active Directory. An Organizational Unit is used to organize users, groups, and computers within a domain, but it does not connect multiple trees. A Domain represents a specific administrative boundary and contains objects such as users and computers, but it does not encompass other domains. A Tree, on the other hand, refers to a hierarchy of domains that are linked in a parent-child relationship but does not encompass multiple trees like a Forest does.