A phenomenon is any observable occurrence.

A phenomenon (from Greek φαινόμενoν, pl. φαινόμενα - phenomena) is any observable occurrence.[1] In popular usage, a phenomenon often refers to an extraordinary event. In scientific usage, a phenomenon is any event that is observable, however commonplace it might be, even if it requires the use of instrumentation to observe it. For example, in physics, a phenomenon may be a feature of matter, energy, or spacetime, such as Isaac Newton's observations of the moon's orbit and of gravity, or Galileo Galilei's observations of the motion of a pendulum.