Plain-language answer: Reactance is the frequency-dependent part of impedance that stores and returns electric or magnetic energy rather than dissipating it as useful power.
Why it matters at the radio
Capacitive reactance is negative and inductive reactance is positive by the usual RF convention. At resonance they cancel at the chosen reference plane, but resistance can still be far from 50 ohms.
What to watch in the field
Read R and X on an analyzer while changing frequency. Element length, loading, height, and nearby conductors can move both the sign and magnitude of X.
The common misunderstanding
Treating every nonzero reactance as simple loss.
Learning boundary
This lesson explains established radio and antenna practice. Current regulations, electrical and building codes, site conditions, and the exact equipment or antenna guide control legal limits, ratings, compatibility, and safety.
