theory (physics), model (physics)
Axiomatizations
Tools
Structural phenomena
Types of quantum field thories
Optics studies light. Light is an electromagnetic phenomenon and it corresponds to the special solutions of the Maxwell equations for the electromagnetic field. Of course, specific methods and applications pertain to optics, which are not used that much in the rest of electromagnetism.
Light has both corpuscular and wave nature. Corpuscular nature is represented by quanta of electromagnetic field, photons.
For applications but also fundamental theoretical consideration there is an important approximation of geometrical optics.