Ciro Santilli distinctly remembers being taught that at basic electrical engineering school during Ciro Santilli's undergrad studies at the University of São Paulo.
It really allows you to do alternating current calculations much as you'd do DC calculations with resistors, quite poweful. It must have been all the rage in the 1950s.
Articles by others on the same topic
Electrical reactance is a measure of how much a circuit impedes the flow of alternating current (AC) due to the presence of inductance and capacitance, rather than resistance. Unlike resistance, which dissipates energy as heat, reactance stores energy in electric or magnetic fields and causes a phase shift between the voltage and current waveforms.