Normalized Power is a power averaging method, measured in watts, that compensates for changes in ride conditions for a more accurate depiction of power expenditure than average power.
Normalized power takes into account the additional stress caused by hills and peaks as well as intervals when compared with a flat ride of the same duration even though the average power would be the same for both rides.
In general, Normal Power is not valid for shorter efforts; in these cases average power should be used instead.