A measure of the strength of the association between two variables. High correlation implies a close relationship and low correlation a less close one. If an increase in one variable results in an increase in the other, then the correlation is positive. Example: there should be a positive correlation between your understanding of maths and your enjoyment of it. If an increase in one variable results in a decrease in the other, then the correlation is negative. The term zero correlation does not necessarily imply no relationship, but merely no linear relationship.