The slope 
of a line obtained using linear least squares
fitting is called the regression coefficient.
Regression Coefficient
See also
Correlation Coefficient, Least Squares FittingExplore with Wolfram|Alpha
References
Kenney, J. F. and Keeping, E. S. Mathematics of Statistics, Pt. 2, 2nd ed. Princeton, NJ: Van Nostrand, p. 254, 1951.Referenced on Wolfram|Alpha
Regression CoefficientCite this as:
Weisstein, Eric W. "Regression Coefficient." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/RegressionCoefficient.html