What is the 70 million year old egg?

Excuse me, but could you please elaborate on this intriguing concept of a "70 million year old egg"? I'm genuinely curious about the origins, nature, and potential significance of such an ancient artifact. Is it a genuine fossilized egg, perhaps belonging to a prehistoric creature? Or is it a metaphorical term used to signify something else entirely? I'm eager to learn more about this fascinating subject.