Parameter Tree:
EARTH SCIENCE > SUN-EARTH INTERACTIONS > IONOSPHERE/MAGNETOSPHERE DYNAMICS > MAGNETIC FIELDS/MAGNETIC CURRENTS

Definition:
An Electromagnetic field (EM field) is the region of space near electric
currents, magnets, broadcasting antennas etc., regions in which electric and
magnetic forces may act, for example on charged particles.


Reference:
http://www-istp.gsfc.nasa.gov/Education/gloss.html