Encounters with extraterrestrials are referred to as close encounters (CE). These can be classified into:

• A close encounter of the first kind (CE1) which involves the sighting of something unidentified within 150 yards.

• A close encounter of the second kind (CE2) is one in which the UFO interacts in some way with the environment, leaving tangible evidence such as a depression in the ground.

• A close encounter of the third kind (CE3) is a visual sighting of an occupant or entity from a UFO, possibly with some interaction with them.

• A close encounter of the fourth kind (CE4) is one involving human abduction by aliens.

• A close encounter of the fifth kind (CE5) would be some form of direct communication with an extraterrestrial being, through channelling or actual contact.