A phenomenon (Greek: φαινόμενo, pl. φαινόμενα) is an observable event or, quite literally, something that can be seen.

It comes from the noun φαινόμενον (phainomenon, df. appearance) and is also related to the verb φαινειν (phainein, df. to show). Its plural is phenomena. Its antonym is lathomenon, meaning "something lying beneath the surface".