what is resonance in rf circuits?

a LC tank can be

Resonance in RF circuits is actually "tuning" the circuit (in EM level) at a certain frequency of an EM signal, thus only "capturing" a specific EM signal in the circuit depending how the circuit is tuned

Added after 1 minutes:

the CIRCUIT mentioned above is referring to a RF circuit **

To understand details about resonance read book by John D. Ryder. Network lines & fields.
Resonances are of two types, series & parallel resonance.
Characteristics of two are different. One give maximum curent at resonance & othe lowest current at resonance.
This concept is used in filters,resonators etc.
resonator circuit is basically LC circuit.(Offcourse R will be there)
Its main use is in tunning. ( ex. receiver,oscillator etc.)