"Virtual machines are virtually taking over the world. By itself
a virtual machine is just a container that describes various
resources such as memory, disk space, processor, and network card,
and allocates them from a physical machine. As with a physical
machine, it's the software bits (the operating system and
applications) that make a virtual machine usable. When you mix a
virtual machine with real software you get a virtual appliance.
Some complete Linux distributions as well as specialized apps are
available as virtual appliances. Thanks to the ease in packaging
one, there's no shortage of virtual appliances around, if you know
where to look.
"Deploying a pre-installed and pre-configured application
appliance is far easier than preparing a system, installing the
app, and configuring and setting it up..."