From LQWiki

A virtual machine is an application that emulates computer hardware in userland. Virtual machines can be used to run other operating systems in the memory of others or to interpret programming languages like Java.

See also

• Emulator
• Emulators and virtual_machines
• JVM -- Java Virtual Machine
• Mono -- includes a "Common Intermediate Language" virtual machine, meaning it can run different kinds programming languages
• Parrot -- A virtual machine specially designed to efficiently execute bytecode for interpreted languages (e.g. Perl or Python)