Residual magnetism and remanence are the same thing. The term residual magnetism is often used in engineering applications. Both terms describe the magnetization, and measure of that magnetism, left behind in a ferromagnetic material after the external magnetic field is removed.

Residual magnetism is a property in which certain amount of excitation remains back in the conductor even after the removal of the magnets.

Yes. The field is provided by the shunt windings, which are connected in parallel with the supply. You may be confusing a motor with a generator, as you cannot start a shunt generatorwithout residual magnetism.

residual magnetism

It depends on the context in which you are referring to it, but basically Residual Magnetism is that magnetism remaining in the core of an electromagnet after the coil current is removed.

In the widest use of the term, it could be used to refer to that magnetism left in a magnetically susceptible substance when it cools past its Curie point, (paleomagnetism is an example of this).