Time series data are measurements of a variable taken at regular intervals over time. Time series are represented as sequences of values like x(1), x(2), … .
A wide class of practically important data are represented as time series: economic and social data, weather records, sports data, to name a few.
Some simple examples of time series are records on monthly unemployment rates, average daily atmospheric temperature, or monthly scores of a football team.
In statistics, time series are often considered as realizations of random series.