In restoration ecology the term biodiversity is widely used to define endpoints, to assess restoration needs, and to monitor restoration success. However, the term is far from clear because different uses of it result in ambiguities and misunderstandings. The appreciation of different thought styles, which are types of worldviews, and different values is crucial for a clearer and more consistent understanding of "biodiversity." Three groups of thought styles with different uses of the term biodiversity can be distinguished. (1) Natural history perceives biodiversity as biotic elements of nature that can be described and classified. (2) Science considers biodiversity as a measurable parameter that is relevant for ecosystem processes and functions. (3) In environmentalism, biodiversity is used in the context of concerns about species extinctions and habitat destructions. Values play a strong role in some perceptions of biodiversity but are negligible in others. Much confusion arises from some people considering biodiversity as something valuable per se and others seeing it as a virtually value-free parameter for the description of ecosystems. Because of different thought styles and values the term biodiversity should be used as a general concept, not as a specific element of nature. Biodiversity is a framework for the variety of life on Earth. Biodiversity in this sense is not measurable. However, specific features of biodiversity, e.g., the species richness of vascular plants, can be quantified. The selection of these features depends on thought styles and values. This implies that "biodiversity as general concept" should be distinguished from measurable "features of biodiversity." Explicit declarations of selected biodiversity features, in every case quantities are in the focus, are inevitable for an unambiguous use of the term.