"Close Encounters of the Second Kind" refers to a classification of UFO encounters where physical evidence is left behind. This can include things like scorched earth, damaged vegetation, or even impressions in the ground. These encounters suggest that an unidentified flying object has interacted with the environment in a tangible way. This term is part of a broader classification system established by J. Allen Hynek, an astronomer who studied UFO phenomena. The system categorizes encounters into different types, with the first kind being sightings of lights or objects, and the third kind involving contact with extraterrestrial beings.