Electromagnetic fields (EMFs, also called electric and magnetic fields), are invisible lines of force that surround all electrical devices. The Earth also produces EMFs; electric fields are produced when there is thunderstorm activity, and magnetic fields are believed to be produced by electric currents flowing at the Earth's core.

Useful links:
Medicinal EMFs: Harnessing electric and magnetic fields for healing and health

Electromagnetic Field Therapies: a Bibliography from Medline

Electromagnetic Field Therapies: other articles