EMF (or Electromagnetic Field) is a broad term which includes electric fields generated by charged particles, magnetic fields generated by charged particles in motion, and radiated fields such as TV, radio, and microwaves.
Electric fields are measured in units of volts per meter or V/m.
Magnetic fields are measured in milli-Gauss or mG. The field is always strongest near the source and diminishes as you move away from the source.
These energies have the ability to influence particles at great distances. For example, the radiation from a radio tower influences the atoms within a distant radio antenna, allowing it to pick up the signal.