Public folder tree (aka public folder root and top level hierarchy - TLH)

A collection of public folders created under the same hierarchical namespace. Previous releases of Exchange server used only a single tree (called: All Public Folders), whereas multiple trees can be defined in Exchange 2000. Each tree is a unit of hierarchy replication and can be replicated to one or more Public MDBs. A Public MDB can host only one tree. Messaging Application Programming Interface (MAPI) clients such as Outlook can only access a single tree called All Public Folders, whereas other clients such as a Web browser or a networking client using the Microsoft Web Storage System can access any tree that is defined. [Exchange 2000]