Characteristic impedance, also known as surge impedance, is a fundamental property of a uniform transmission line. It represents the ratio of the voltage to the current for a single wave traveling along the line in one direction. Unlike standard impedance, it is an intrinsic property of the line itself, determined solely by the line's physical geometry and materials (specifically, its inductance and capacitance per unit length), not its length or the load it's connected to. For lossless transmission lines, characteristic impedance is a purely resistive value.