They are the same. They both use air as the medium to dump heat to. However, and air cooler uses the air inside the case as the sink. Liquid coolers use water to transfer the heat to the radiator, they then dumps to air usually cooler air, external to the case.
Water also gas a much higher specific heat capacity than air so can usually remove heat from a hot CPU more quickly.
With an air cooler, excellent case cooling is important, something that people often forget.
Those mm sizes are radiator lengths.