Electromagnetic waves with radio frequencies (RF) are part of the non-ionizing electromagnetic spectrum in the range 10kHz - 300GHz (although different sources vary in this range definition). In our ECI we involve also lower frequencies (30Hz - 10kHz).
Electromagnetic waves are also called electromagnetic radiation or radiation.
Electromagnetic Radiation is emitted in discrete units called photons and has at the same time properties of waves. It travels through space at the speed of light.
Radiation has an electro and a magnetic field component. This forms a so called electromagnetic field (EMF). A Radiofrequency electromagnetic field (RF EMF) is a field of a wave in the radio spectrum.
When we measure the "strength" of those fields, we measure power density expressed in W/m2 (Watt per square meter).
Very confusing nomenclature
The classification system has its origin in radar work during Second World War. A lack of standardization has succeeded in confusing just about everyone. Wartime secrecy concerns were so great that the radar design community didn´t even standardize nomenclature with engineers involved in other communications research elsewhere. We are still living with the resulting legacy of confusion:
R. Timothy Hitchcock, Nonionizing Radiation Committee
Radiowaves frequency: 3 kHz – 300 MHz
Microwaves frequency: 300 MHz – 300 GHz
Radiowaves frequency: < 3 GHz
Microwaves frequency: 3 GHz – 300 GHz
Radiowaves frequency: 3 Hz – 1 GHz
Microwaves frequency: 1 GHz – 300 GHz
Radiowaves: 3MHz – 1 GHz
Microwaves: 1 GHz – 110 GHz
ITU Radio Regulations
Radio spectrum: 3 Hz – 3,000 GHz
Below about 10 kHz it is practically not possible to use antennas, so very few radio systems use frequencies below this, because antennas should be very large (kilometers in diameter).