The slope of a graph represents the rate of change of the dependent variable (in this case, displacement) with respect to the independent variable (in this case, time).
Since velocity is defined as the rate of change of displacement with respect to time, the slope of a displacement vs. time graph directly represents the velocity of the object.
Mathematically, the slope of a graph is calculated by dividing the change in the dependent variable by the change in the independent variable:
$$ Slope = \frac{Change\ in\ Displacement}{Change\ in\ Time} $$
This ratio represents the average velocity of the object over the time interval considered. Velocity can be positive, negative, or zero, depending on whether the object is moving in the positive direction, the negative direction, or not moving at all.
