Appliance

"A virtual appliance is a virtual machine image designed to run on a virtualization platform (e.g., VirtualBox, Xen, VMware Workstation, Parallels Workstation)."
http://en.wikipedia.org/wiki/Virtual_appliance

So a Tiki appliance is Tiki designed to run on a virtualization platform.

See TikiWikiVMwareAppliance

Some appliance providers:
http://www.jumpbox.com/app/tikiwiki
http://www.standingcloud.com/network/tikiwiki