The phrase "regression slope" refers to the measure of the direction and steepness of a line in a regression analysis. It tells us how much the dependent variable changes when the independent variable increases by one unit. Full definition
We examined regression slopes within BSI quartile ranges. (academic.oup.com)
However, Dessler also plots climate model results and finds that they also simulate negative time regression slopes when cloud changes lead temperature changes. (skepticalscience.com)
Most of the data visually sloped downward but the outliners when weighted made the overall regression slope up! (wattsupwiththat.com)