Secant Lines: "A secant line is a straight line joining two points on a function. (See below.) It is also equivalent to the average rate of change, or simply the slope between two points."
Secant Note: Secant line = Average Rate of Change = Slope
Tangent Lines: "A tangent line is a straight line that touches a function at only one point. The tangent line represents the instantaneous rate of change of the function at that one point. The slope of the tangent line at a point on the function is equal to the derivative of the function at the same point."
Tangent Note: Tangent Line = Instantaneous Rate of Change = Derivative