A secant line is a line that intersects a curve at two or more points. The word "secant" comes from the Latin word "secare," meaning "to cut". In the case of a circle, a secant intersects the circle at exactly two points. Secant lines may be used to approximate the tangent line to a curve at some point P, if it exists. To do this, define a secant to a curve by two points, P and Q, with P fixed and Q variable. As Q approaches P along the curve, if the slope of the secant approaches a limit value, then that limit defines the slope of the tangent line at P. The secant lines PQ are the approximations to the tangent line. In calculus, this idea is the geometric definition of the derivative. The use of secant lines to iteratively find the root of a function is known as the secant method. In abstract mathematics, the points connected by a secant line can be either real or complex conjugate imaginary.