I see many questions About antenna impedance/resonance ect.
in simple words about the complicated.
Z -complex impedance
R – active resistance
X – reactive impedance (j – is the imaginary unit, and is used instead of
i
in this context to avoid confusion with the symbol for electric current.)

Z=R+(-)jx
Swr 1:1.0 – 50=50+(-)0

remember swr this is unnecessary indicator.

Antenna Resonance in simple words this jx =0 (and then you see real antenna impedance)

For example:
Dipole z=50ohm on 7100, but z = (R)70-(jx)20, and we have for example swr 1,2
But real resonance for example on 6900 where minimum jx = +2.5 and R = 65.
Swr on 7100 ~1.2
Swr on 6900 ~1.2 BUT 6900 its antenna resonance.

UR4UNR