a cliché

A cliché is a truism so trite, hackneyed and overused that it has lost all bite. An example? Most of the well-known proverbs fit the bill. A penny saved is a penny earned. Time is money. It's always darkest before the dawn. Well, do'h.

Remember cliché is a french word. It means the picture taken with the first photographic devices.
At the time people posed in a stereotyped way, always the same.
So today cliché is some word, sentence, expressing a commonplace.

When joking, "blonde is one neuron person" is a cliché.

In my opinion it is a phrase used in works such as essays, stories and poems that has been used so many times that it is no longer original and creative.. for example "full of terror", "beads of sweat"

I didn't know that, Francis. That's quite interesting.