Why airplane windows have that tiny hole

That tiny dot near the bottom of an airplane window is a deliberate bleed hole. Passenger windows use several acrylic panes; the hole lets air move between the cabin and the space between the panes, so the outer pane carries most of the pressure difference. 12

At cruising altitude, Honeywell says cabin pressure is about 11–12 psi, while the outside air is much thinner. The same air path also helps reduce moisture trapped between the panes. 34