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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 they have a relation with 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
Electromagnetism underlies much of what we experience, far beyond our electric service, electronics, etc. When digging into detail of the way things work, electric force is basic to atoms (nuclei and electrons), as well as their interconnection (molecules, crystals, anything solid), and their reactions (chemical reactions, including fire and explosions which are the basis for internal combustion engines, jet and rocket engines). What is not electromagnetism is gravity, nuclear reconfigurations such as fission and fusion, and radioactivity.