Correlation

The correlation between two variables describes the degree of their statistical, typically linear, relationship. This relationship is non-directional, meaning it does not indicate whether, or which, variable causes the other. If an increase in one variable tends to be associated with an increase in the other, the variables are said to be positively correlated. Conversely, if one variable tends to decrease while the other increases, they are said to be negatively correlated.

A typical example: The daily maximum temperature and the number of ice creams sold per day are usually positively correlated.

In the context of time series, Autocorrelation and Cross correlation are important forms of correlation.