The Overpopulation Crisis of 17231 was an event in Ferenginar history, in which the Ferengi population of the planet peaked at several billion. During this period, it was said (likely apocryphally) that no raindrops ever hit the ground because there were so many Ferengi heads in the way.
The Overpopulation Crisis was ended with the alleged discovery by Ferengi explorer "Mad Zook" of the planet Chimera Pi, and of massive deposits of latinum there. Rumors of other similar worlds followed, inducing billions of Ferengi to leave their homeworld to seek their fortunes.
It was later discovered that these rumors had originated with the Ferengi Office of Population Control. (DS9 novel: Legends of the Ferengi)