R squared
R^2 is the percentage of variation in the response that is explained by the model. It is calculated as 1 minus the ratio of the error sum of squares (which is the variation that is not explained by model) to the total sum of squares (which is the total variation in the model).
R^2 is the percentage of variation explained by the relationship between two variables. R is the actual correlation. R also tells that is it positive or negative correlation.