Application Virtualization

The term “application virtualization” describes the process of compiling applications into machine- independent byte code that can subsequently be executed on any system that provides the appropriate virtual machine as an execution environment. The best known example of this approach to virtualization is the byte code produced by the compilers for the Java programming language (http://java.sun.com/), although this concept was actually pioneered by the UCSD P-System in the late 1970s (www.threedee.com/jcm/psystem), for which the most popular compiler was the UCSD Pascal compiler. Microsoft has even adopted a similar approach in the Common Language Runtime (CLR) used by .NET applications, where code written in languages that support the CLR are transformed, at compile time, into CIL (Common Intermediate Language, formerly known as MSIL, Microsoft Intermediate Language). Like any byte code, CIL provides a platform-independent instruction set that can be executed in any environment supporting the .NET Framework.

Application virtualization is a valid use of the term “virtualization” because applications compiled into byte code become logical entities that can be executed on different physical systems with different characteristics, operating systems, and even processor architectures.
Taken from : William Von Hagen "Professional Xen Virtualization" 2008