An inverter aircon is a type of air conditioning unit that uses adjustable speed to control the compressor of the equipment, providing the best performance to the user. It adjusts its processes based on the current temperature in the room, making it more versatile and energy-efficient than non-inverter aircon units.

On the other hand, "inverter grade" aircon is a term that is not commonly used in the air conditioning industry. It is not a standard term, and there is no clear definition of what it means. Some people use it to refer to aircon units that are not true inverter aircon units but have some inverter-like features, such as the ability to adjust the compressor speed.

In summary, an inverter aircon is a type of air conditioning unit that uses adjustable speed to control the compressor of the equipment, while "inverter grade" aircon is a term that is not commonly used in the air conditioning industry and does not have a clear definition.