What is a secant line?

A secant line is defined as a line that intersects a curve at two or more points. This concept is particularly important in calculus, where it is used to approximate the slope of the tangent line at a particular point on the curve. By taking the average rate of change between the two intersection points, the secant line provides a broader view of the function's behavior over that interval.

In contrast, the other choices describe different types of lines in relation to curves. A line that touches a curve at a single point is referred to as a tangent line, which is distinct from a secant line. A line that is tangent to a curve does not cross the curve but merely touches it at that point. A line parallel to the axis would not necessarily intersect the curve at multiple points and, therefore, does not fit the definition of a secant. Understanding these distinctions is crucial in the study of functions and their graphical representations.