A geomagnetic storm is a short-term disruption of the magnetic field
surrounding Earth, i.e., a temporary change from its usual
state, typically returning to normal in a few days. Such storms
are invariably from influence of the Sun, and can be thought
of as a solar storm that specifically affects the Earth's
magnetic field, e.g., due to solar activity
such as a coronal mass ejection (CME), etc. (if it happens to face Earth).
Such storms can affect radio communication, power, satellites,
etc., and often include auroras.