Desponds were creatures that fed off hope. They resembled dogs with three legs and a tentacle that protruded from its mouth, which clung to peoples' throats. They also had razor-sharp teeth. The tentacle, when stuck to throat of a person, sucked away hope until people despaired and claimed there was no hope of escape.
There were thirteen Desponds in Terminal 4000. The terminal was closed because of them. There was no transportation there because of the danger. The Eleventh Doctor lost hope after being fed on. Amy had to help him. (PROSE: Terminal Of Despair)