appliance in release-notes

["Domingo Becker" <domingobecker gmail com>]

What is the meaning of appliance in the context of release-notes ?
release-notes mentions an appliance creation tool, a tool to create
appliance images from a kickstart file.
In this context, it is an installer for me. But, what would be the
right meaning of it?
What is an appliance image used for?

regards

Domingo Becker (es)