1. The number and variety of organisms in a given locality, community, or ecosystem at a given time.
2. In different contexts it may denote: the number of different species present in a given environment (species diversity); the genetic diversity within a species (genetic diversity); the number of different ecosystems present in a given environment (ecological diversity).

High biodiversity is typical of complex and highly productive ecosystems; such as, tropical rain forests, where a small area can contain many different species of animals, plants, and other organisms.

Biodiversity is often used as an indicator of the health of such ecosystems.