The document discusses self-induced emf, self-inductance, mutually induced emf, and mutual inductance. It states that self-induced emf is proportional to the rate of change of current through a coil and self-inductance is the proportionality constant. Mutually induced emf occurs when the magnetic flux passing through one coil changes due to a changing current in another nearby coil, and mutual inductance is the proportionality constant between the induced emf and rate of change of current. The coupling coefficient k describes the degree of coupling between two coils and is defined as the ratio of mutual flux to self flux.