In field theory (physics), two fields are coupled if they are interacting with each other.
Coupling (physics) Wikipedia
Of special interest is the coupling of two (or more) vibratory systems (e.g. pendula or resonant circuits) by means of springs or magnetic fields, etc. Characteristic for a coupled oscillation is the effect of beat.
The concept of coupling is particularly important in physical cosmology, in which various forms of matter gradually decouple and recouple between each other.
Coupling is also important in physics for the generation of plasmas. In electrical discharges, the coupling of an exciting field and a medium creates plasmas. The quality of the coupling of an exciting field of given frequency to a charged particle depends on resonance.