An animal that is endangered is close to extinction — meaning there aren't very many of them left in the world.
This word is used mostly to describe animal species that are not doing very well: animals usually become endangered because of over hunting or the destruction of their habitat. Environmental groups and animal-lovers try to help endangered species survive. Outside of the animal kingdom, you can say anything that seems to be dying out is endangered, like good manners, phone booths, or the art of letter writing.
