Types of pattern

Trend Seasonal variation
Trend refers to long-term increases and decreases in the values.
This is often evident in monthly or quarterly data and refers to a pattern that is repeated each year.
Cyclic variation (autocorrelation) Random fluctuations
This arises when values are similar to adjacent values, making irregular waves or cycles .
These are 'ups and downs' in a time series that do not correspond to trend, seasonal variation or autocorrelation.

Most time series show more than one of these patterns to some degree.