Why is there a hole in airplane windows?

I always wondered this- why is there a tiny hole in the windows? We learned this in heat transfer- air is a great thermal and convective insulator. So air flows in between the first window (inside the cabin) and the second window (in contact with the outside air) to serve a few purposes- regulate cabin pressure, maintain temperature control, and prevent moisture from forming on the cabin windows. From fluid mechanics, we know from Bernoulli’s Principle that at any point along a streamline in a fluid, if the velocity is higher, the pressure will be lower.

Hole in Airplane Windows