Flux linkage refers to the total magnetic flux that is linked with a coil or a circuit due to the magnetic field produced by another coil or source. It is a critical concept in understanding how energy is transferred between inductively coupled circuits, as it describes the interaction between magnetic fields and electric currents in a system. The amount of flux linkage determines the induced electromotive force (EMF) when the magnetic field changes over time, which is central to various applications like transformers and inductors.