Definition of phenomenon. 1 plural phenomena : an observable fact or event. 2 plural phenomena. a : an object or aspect known through the senses rather than by thought or intuition. b : a temporal or spatiotemporal object of sensory experience as distinguished from a noumenon.

Thus, the term phenomenon refers to any incident deserving of inquiry and investigation, especially events that are particularly unusual or of distinctive importance. A comparison between a candle flame on Earth (left) and in a microgravity environment, such as that found on the International Space Station (right).