Properly speaking electromagnetic refers to the electromagnetic spectrum including radio waves, microwaves, light, x-rays and gamma rays. These are all produced in different ways. Detected in different ways. Nature of challenges differ.
Electromagnetics is a term that covers all theoretical and practical subjects of itself..
Engineering side of this huge physical phenomena addresses practical applications rather than theoretical one.
Antennas,Transformers,Waveguides,Transmission Lines,Electric Motors etc. is the concern of this practical side.
Electromagnetics is the theoretical background of RF engineering, "Engineering Electromagnetics" is the title of lectures and text books presenting the subject to engineers.