The Advisers Group

JeOS, pronounced juice, is a customized operating systems that is normally configured specifically for virtual appliances.

JeOS includes only the operating system components required to support a particular application. Typically the JeOS only contains a web and database server. This makes the appliance smaller, and more secure than an application running under a full OS.

Ubuntu has some great information on their Ubuntu JeOS and Novell currently has is SUSE JeOS in Beta.