What is the "Rule of 80" in Connection with Israel?

I am not a Muslim. In discussions about Israel/Palestine with Muslims online, a number of them have referenced a "rule of 80" in connection with Israel. From the context of the discussions, it seemed to be that they were saying that Israel would last only 80 years. Does anyone know the source of this "rule of 80"? Is there any authority for interpreting this source as applying to the modern state of Israel?