Afunction which gives the slope of a curve; that is

Tangent

Explanation:

The slope of a curve at a point is equal to the slope of the straight line that is tangent to the curve at that point.The slope of a curve y = f(x) at the point A means the slope of the tangent at the point A. Tangent of a curve tells us the rate of change at a particular instant. We write y = f(x) on the curve since y is a function of x. That is, as x changes, y also changes.