A Contactee is a person who has undergone a close encounter of the fourth kind - they have communicated with a being connected with an Unidentified flying object in some way (even if the UFO is never seen but there is reason to make the connection).
There are two main types of contactee experience. In alien abduction, the contactee reports being taken on board a UFO against their will, and often subjected to invasive medical procedures; the experience is usually (and understandably) extremely stressful. A more benign experience, which was the dominant form in the 1950s and 1960s, describes benevolent space brothers offering wise warnings about nuclear war and other problems being faced by the Western world at the time. these beings were said to be from planets in our solar system; since space probes showed these worlds to be lifeless, the space brothers have claimed to come from further away (the Pleiades being an oft-quoted location).