Biodiversity is defined as 'the variability among living organisms from all sources, including, inter alia, terrestrial, marine, and water aquatic ecosystems, and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.
Definition as per the United Nations Earth Summit, Rio de Janeiro, in 1992, quoted in "Intro To Env Engg (Sie), 4E Davis", p. 40