(追記) (追記ここまで)
Instantaneous Rate of Change
The rate of change at a particular moment. Same as the value of the derivative at a particular point.
For a function, the instantaneous rate of change at a point is the same as the slope of the tangent line. That is, it's the slope of a curve.
Note: Over short intervals of time, the average rate of change is approximately equal to the instantaneous rate of change.
See also