Square of the correlation coefficient . The proportion of the variability in one series that can be explained by the variability of one or more other series in context of regression. A measure of the quality of fit. 100% R-square means perfect predictability.
R SQUARED (R2)
Meaning of R SQUARED (R2) in English
Campbell R. Harvey. Hypertextual finance English glossary. Английский словарь гипертекстовых финансов. 2012