electromagnetism

Electromagnetism (EM or as an adjective, electromagnetic) refers to electricity and magnetism and their interaction. Electromagnetic theory describes their behavior, and electromagnetic radiation (EMR) is visible light and similar radiations, the term making clear their relation to electricity and magnetism.

For a while, electromagnetism was considered one of the four fundamental physical forces. This was after Maxwell's equations showed how interdependent electric and magnetic forces are, being two aspects of the same physical rules. A later, the electroweak theory showed EM to be similarly-related to the weak force. Though this latter combination is accepted, EM and the weak force are very often cited and treated as separate fundamental forces since the relationship is seldom of any significance in current observation and experiment.