Coefficient of Determination (R-Squared)

The coefficient of determination measures the percentage of variation in Y that is explained by the model and will be between 0 and 1.

To explain the R-squared (coefficient of determination), in this video the author compares it to the standard error of estimate (a measure of the line's accuracy) and the correlation (the square root of the coefficient of determination). All three are measures of the line's fit to the data.