The word radiation usually refers to electromagnetic radiation. Electromagnetic radiation is energy that spreads through space or through various types of matter in the form of waves.
Radiation is emitted by many different sources that are man-made (e.g. antennas/base stations) or natural (e.g., the sun).
Electromagnetic radiation is a combination of electric and magnetic fields – electromagnetic fields – created by charges and electric currents.
Electromagnetic radiation is described by physical attributes that include frequency, wavelength and indicating the intensity of radiation.
Matter absorbs electromagnetic radiation in the form of tiny particles of energy called photons. In this manner, in our visual system, cells in the retina of the eye absorb photons of visible light and translate them into images.
The magnitude of absorption of electromagnetic radiation by matter depends both on the attributes of the electromagnetic radiation and on those of the absorbing matter.