Answer:
Speed 
Step-by-step explanation:
On a distance - time graph, the slope of the line indicates the speed of the object. 
Speed is the rate of change of distance with time. 
 Speed = 
 
 
 Now, the slope is the change in distance with the change time which is commensurate with the speed equation. 
For a displacement - time graph, the slope is the velocity. 
 Therefore the slope of a distance - time graph is its speed.