• A time series is a set of measurements of a variable taken at regular intervals of time.
• A time plot can show variation over time which can take the form of
  • A trend (long-term change)
  • Seasonal variation (change occurring during specific time periods)
  • Irregular fluctuations (changes caused by unusual events)
  • Cycles (distinct up and down movement which is less regular than seasonal variation and not explained by seasonal effects).