Biodiversity is the variety of all forms of life on Earth. It is a measure of genetic variation within species, the variety of species within ecosystems, and the variety of ecosystems on the planet. Variety is usually greater in warm areas; on land these are generally closer to the equator, and in the oceans along coasts in the Western Pacific, where sea surface temperatures are highest. Biodiversity tends to cluster in "hotspots" and has been increasing over time, but is threatened by biodiversity loss.
See also Wikipedia article on Biodiversity