As the name implies, Undercounter Ice Makers are designed with front ventilation to allow them to be built in or between cabinetry. Built-in ice makers should be installed by a professional plumber. They take a permanent water line, and some of them also need a drain line. These can store much more ice than a portable model, and can keep it frozen for longer periods of time.
The vast majority of consumer oriented built-in ice makers do not offer a refrigerated storage bin. At some point the ice produced will melt and the resulting water may need to be drained from the machine. The most common way to achieve this goal is to establish a permanent gravity drain line. The gravity drain line will exit the back of the machine and carry the water to a nearby drain located below the ice maker.