From AMS Glossary
(Also called moving average, overlapping mean, running mean.) A smoothed representation of a time series derived by replacing each observed value with a mean value computed over a selected interval.
For example, if the observations are of daily maximum temperature and the selected interval is five days, then the value assigned to 5 February is the mean of the daily maxima from 3 through 7 February, etc. Consecutive means are used in smoothing to eliminate unwanted periodicities or minimize irregular variations.