An arboretum is a small garden area on a starship, which is designed to provide Starfleet officers and enlisted personnel with a comfortable outdoors space in which they can relax. An arboretum can be as small as a single tree with a bench on some starships, or in some cases of larger starbases, run to an entire self-enclosed forest. Often these areas are equipped with holographic projectors to help further the "outdoor" or rustic experience.
Most Starfleet vessels, apart from the smallest, feature an Arboretum. They are maintained by the Science Department.