Secant
A straight line through two points on a curve; its slope is the average rate of change between them.
The straight line through them is a secant, and its slope is the average rate of change: (f(x + h) − f(x)) / h For f(x) = x² from x = 1 to x = 2, that is (4 − 1) / 1 = 3.
See it in action
Try secant hands-on in the lesson Derivatives, part of the The maths behind AI course.