The line impedance (characteristic impedance) of a uniform transmission line, is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections.
The wave impedance of an electromagnetic wave is the ratio of the transverse components of the electric and magnetic fields (the transverse components being those at right angles to the direction of propagation). For a transverse-electric-magnetic (TEM) plane wave traveling through a homogeneous medium, the wave impedance is everywhere equal to the intrinsic impedance of the medium.