IR

An instrument rating is technically not a pilot certificate, but an add-on rating that allows an airplane or helicopter pilot to fly in weather with reduced visibility such as rain, low clouds, or heavy haze. When flying in these conditions, pilots follow instrument flight rules (IFR). The training provides the skills needed to complete flights with less than the required VFR minimums.

NR

Such as instrument rating, Night rating is technically an add-on to be able to fly at night.