R^{2}.
Taraday, M., & Wieczorek-Taraday, A. (2018). R^{2}. In B. B. Frey (Ed.), The SAGE encyclopedia of educational research, measurement, and evaluation (pp. 1362-1363). SAGE.
This is the coefficient of determination used in a regression analysis. The R^{2} is used to represent that amount of variance in the dependent variable, which is predicted by the independent variable.