Professional Answer: For practical purposes in power systems, the terms characteristic impedance and surge impedance are often used interchangeably. However, there is a technical distinction. Characteristic impedance is a more general term that can be a complex number, accounting for line losses. Surge impedance, by definition, specifically refers to the characteristic impedance of a lossless transmission line (i.e., with zero resistance and conductance). In this ideal case, the characteristic impedance simplifies to a real number, calculated as the square root of the ratio of the line's inductance to its capacitance per unit length (Z0=L/C).