It is called the intake air preheat hose. About a minute after a cold start, the exhaust manifold is already warming, so this hose allows some of the combustion air to be warmed faster for better fuel atomization and ultimately better emissions for the first five or ten minutes of cold-weather driving.

There's a thermostatically operated door in the airbox where it ends up. It is supposed to remain shut unless the air is very cold, but the thermostat does not last long allowing it to remain open even when hot. The fabled result is extremely warm air reduces the life of the expensive mass airflow meter.

So, many of us brick owners do away with the shiny corrugated aluminum pipe, saving our mass airflow meters from destruction, as long as your air control board doesn't check for its presence.