Slope describes the steepness of a line and is defined as the rise over the run between two points on a line. It can be positive, negative, zero, or undefined. To determine the slope of a line, two points are identified and the change in y-values (rise) is divided by the change in x-values (run). The slope-intercept form of a linear equation is y = mx + b, where m is the slope and b is the y-intercept. To graph a line using slope-intercept form, the y-intercept is plotted and then additional points are determined by applying the slope using rise-over-run from the previous point.