An arboretum is a botanical collection composed exclusively of trees of a variety of species. Originally, they were mostly created as a section in a larger garden or park for specimens of mostly non-local species, but many modern arboreta are in botanical gardens as living collections of woody plants and are intended at least in part for scientific study. The term "arboretum" comes from the Latin word for a place planted with trees, not necessarily in this specific sense. Some key features of arboreta include:

• Tree-focused: Arboreta are botanical gardens specializing in trees or woody plants.

• Scientific study: Many arboreta are intended for scientific study, and some conduct scientific research and conservation.

• Collections: Arboreta have collections of trees of a variety of species, and some have collections of more than 100 species, varieties, or cultivars of trees or woody plants.

• Public outreach and education: Arboreta often engage in public outreach and education, including visitor access that includes some level of public access and at least one public event or educational program each year focused on trees or arboretum purposes.

• Collaboration: Arboreta can collaborate with existing or potential arboreta or even start one of their own.

Arboreta can be found in all shapes and sizes and can be traditional or non-traditional. A traditional arboretum is one whose primary purpose is to be a tree-focused public botanic garden, while non-traditional arboreta are part of organizations or institutions whose primary purpose is other than existing solely as an arboretum, but their site includes an arboretum. Examples of traditional arboreta include The Morris Arboretum, U.S.A.; Westonbirt, The National Arboretum, UK; and Arboretum Wespelaar, Belgium. Examples of non-traditional arboreta include municipal tree collections or parks, school campuses, cemeteries, zoos, and historical properties or estates.