IUCN is the International Union of Conservation of Nature and Natural resources which are now called world conservation union (WCU). It maintains a red databook or red list which is a catalogue of taxa facing a risk of extinction.
Endangered species are those facing a high risk of extinction in the wild in the near future due to a decrease in its habitat, excessive predation or poaching. The percentage of endangered species in the list of threatened ones is 19% mammals,17% birds, 21% reptiles, 22% amphibians and 19% angiosperms. In India, the number is 54 animals and 113 plants, e.g., red panda, Bentinckia nicobarica.

Critically Endangered: The taxon is facing a very high risk of extinction in the wild and can become extinct any moment in the immediate future, e.g., Sus salvinus (Pigmy Hog), Berberis nilghiriensis, Red panda.

Vulnerable: Presently the population is sufficient but is undergoing depletion due to some factors so that it is facing a risk of extinction in medium-term future, e.g., Antelope cervicarpa.

Extinct: The taxon has been completely eliminated or died out from earth, e.g., Dodo.