Virtualization: A Manager’s Guide – O’Reilly Media
dmoz.org lists VirtualBox et al. just as Computers: Emulators: Intel x86 Architecture.
They show this in “see also”: Computers: Software: Operating Systems: x86.
The author: Dan Kusnetzky.
From the TOC:
- A Model of Virtualization (the Kusnetzky Group model of virtualization)
 - Access Virtualization: Providing Universal Access
 - Application Virtualization: Application Isolation, Delivery and Performance
 - Processing Virtualization: Doing System Tricks // Oracle’s VirtualBox goes here
 - Network Virtualization: Controlling the View of the Network
 - Storage Virtualization: Where Are Your Files and Applications?
 - Security for Virtual Environments: Guarding the Treasure
 - Management for Virtual Environments
 - Using Virtualization: The Right Tool for the Job
 
Very, very interesting reading!
Will be a good source for clarifying, what kind of virtualization is actually meant under certain circumstances. Very good reference material!