The First Kind – Observing a UFO
The Second Kind – Physical evidence of a UFO or Alien
The Third Kind – Contact with an alien.
This terminology was coined by UFO researcher and professor J. Allan Hynek in a section of his book The UFO Experience titled Close Encounters.
Dr. Hynek was a technical advisor in Steven Spielberg’s 1980 classic film Close Encounters of the Third Kind. He was paid a small fee and even made an uncredited cameo appearance as one of the researches in the climax of the movie.
For your entertainment, here is a translation of the musical interaction scene at the end of the film (warning: language may not be suitable for all viewers).