Phenomenon (noun)

1. A fact, occurrence or situation that is observed to exist or happen.
2. A rare, significant, or unusual event or circumstance.
3. A thing or event that is remarkable or noteworthy.

Origin:

From late latin phaenomenon, from greek φαινόμενον (phainomenon), from φαίνεσθαι (phainesthai, "to appea.r")

Examples:

1. The phenomenon of global warming.
2. The northern lights are a natural phenomenon.
3. The phenomenon of the stock market crash.