Definitions for "Characteristic Impedance"
The impedance of a cable supposing it had infinite length. It is equal to the value of the terminator resistor that should be used. The characteristic impedance is not the same as the cable's DC resistance.
A compound measurement of the resistance, inductance, conductance and capacitance of a transmission line expressed in ohms.
In a transmission cable of infinite length, the ratio of the applied voltage to the resultant current at the point the voltage is applied, or the impedance, which makes a transmission cable seem infinitely low, when connected across the cable's output terminals. For a wave-guide, it is the ratio of voltage to the current at certain points on a diameter, when the wave-guide is match-terminated.