Close Encounters:
Close Encounter of the 1st Kind(CE1): When a UFO is seen at close quarters for a prolonged period of time. A witness is able to give a detailed description of its shape, color, and behavior.
Example: See The Exeter Incident
Close Encounter of the 2nd Kind(CE2): Similar to a CE1 but the UFO causes vegetation to sway and may burn plants or the ground from engine blasts. Marks are usually unique and not identical to marks left by farm machinery or equipment.
Example: See Robert Taylor Incident
Close Encounter of 3rd Kind(CE3): A CE1 and CE2 combined along with the appearance of occupants or a crew of the UFO. They are sometimes referred to as Ufonauts. Most witnesses who claim to have a CE3 are convinced they’ve met an alien of some kind.
Example: See The 1964 Sorroco UFO Encounter
Close Encounter of the 4th Kind: When a witness interacts or communicates with the alien in some way.
Example: See The Betty and Barney Hill Incident
Close Encounters of the 1st, 2nd, and 3rd are generally the only three generally accepted by researchers. There are also 5th, and 6th kinds however, since there are numerous descriptions of what they are, they are mostly ignored by researchers. The Betty and Barney Hill Incident is more of an alien abduction than a Close Encounter case however given what classifies as a Close Encounter of the 4th Kind it is the best example given.