The Pearson Product-Moment Correlation Coefficient (also known as r) is a value that measures the correlation between two variables $\mathit{X}$ and $\mathit{Y}$.
The coefficient value ranges from $-1$to $1$, where a positive value represents a positive correlation, a value of $0$ represents no correlation and a negative value represents a negative correlation.
Values of ±$1$ are considered total correlations and only occur when all of the data points lie on a straight line.
Data sets with values of r near 0 are considered to have weak correlations, while data sets with values of r near $\+1$ or $-1$ are considered to have strong correlations.