Extinct in the wild

A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as known only by living members kept in captivity or as a naturalized population outside its historic range due to massive habitat loss.
Examples.
Examples of species and subspecies that are extinct in the wild include:
The Pinta Island tortoise ("Geochelone nigra abingdoni") had only one living individual, named Lonesome George, until his death in June 2012. The tortoise was believed to be extinct in the mid-20th century, until Hungarian malacologist József Vágvölgyi spotted Lonesome George on the Galapagos island of Pinta on 1 December 1971. Since then, Lonesome George has been a powerful symbol for conservation efforts in general and for the Galapagos Islands in particular. With his death on 24 June 2012, the subspecies is again believed to be extinct. With the discovery of 17 hybrid Pinta tortoises located at nearby Wolf Volcano a plan has been made to attempt to breed the subspecies back into a pure state.
Not all EW species are rare. An example is the Brugmansia family, where all seven species are widely cultivated but none are found in the wild. Ultimately, the purpose of preserving biodiversity is to maintain ecological function, so when a species exists only in captivity, it is ecologically extinct.
Reintroduction.
Reintroduction is the deliberate release of individuals into the wild, from captivity or from other areas where the species survives. However, it may be difficult to reintroduce EW species into the wild, even if their natural habitats were restored, because survival techniques, which are often passed from parents to offspring during parenting, may have been lost. 
An example of a successful reintroduction of a formerly EW species is Przewalski's horse, which as of 2018 is considered to be an endangered species, following reintroduction started in the 1990s.