Arc impedance
The AC resistance of the electric arc, which dynamically results from the ratio of voltage to current variations during the process.
The term "arc impedance" is unusual in workshop practice and is misleading. What you mean is simply the electrical resistance of the arc, which results from voltage and current. This resistance is not constant but changes constantly with the arc length. For you as a welder, the most important thing is: the arc must burn stably. You achieve this by keeping the distance between electrode and workpiece constant and setting the machine to the correct current for your material. If the arc flickers or breaks off, it's usually due to too long an arc length or wrong current, not some "impedance." Adjust the parameters until the arc burns calmly and evenly, then the weld quality will be right.