At the subatomic level, electromagnetism is defined as the force between electrically charged particles. It is considered one of the fundamental interactions of matter. Oscillating electrical charges result in electromagnetic waves.
On a larger scale, electromagnetism is the creation of a magnetic field from the movement of electrical charges. It usually concerns the use of electric current to make electromagnets, which is called electrodynamics. Another effect is electromagnetic induction, which is using an electromagnet or changing magnetic field to induce an electric current.