Any species that is highly likely to become extinct in the near future (as categorized by the International Union for Conservation of Nature)
The International Union for Conservation of Nature and Natural Resources is an international organization that is involved in data gathering and analysis in the field of natural conservation and sustainable use of natural resources. They proposed various criteria that they use to determine a threatened species. A threatened species is one that is likely to become an endangered species in the near future throughout all or a significant portion of its range. Accordingly, threatened species is further categorized into: vulnerable species, endangered species, and critically endangered species. Vulnerable species, compared to other categories, are the least at risk of extinction. The endangered and the critically endangered species are more at risk of being wiped out altogether. They have the so-called Red List, which holds a comprehensive inventory of the global conservation status of biological species.
An endangered species is a species that is likely to become extinct unless conservation measures and practices are (continuously) implemented, e.g. forbidding hunting, creating preserves, maintaining sanctuaries, etc. Some of the species considered as endangered are African penguin, Asian elephant, blue whale, bonobo, tasmanian devil, proboscis monkey, green sea turtle, and so on.