To adjust data or statistics to remove seasonal variations, so patterns and trends can be seen more clearly.
From de- (removing) + seasonalize (to make seasonal). Modern technical term created in economics and statistics.
Economists deseasonalize data because Christmas shopping skews December numbers—by smoothing out seasonal bumps, they can see if the economy is truly improving or declining.
Complete word intelligence in one call. Free tier — 50 lookups/day.