Biological diversity -- or biodiversity for short -- is a broad concept that seeks to describe the variety and richness of life in a particular place. It spans various scales of life, from species and genetic diversity to the diversity of types of ecosystems. And it can span geographic scales, from the diversity in one’s backyard to the biodiversity of nations or the whole Earth.
Here are typical definitions:
The variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems, and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.
Convention on Biological Diversity
Biodiversity is the variability within and among all living organisms and the ecological complexes in which they occur. Biodiversity includes ecosystem or community diversity, species diversity, genetic diversity and the ecological and evolutionary processes that sustain it.
The Nature Conservancy’s Conservation Gateway