Energy emitted in the form of waves or particles.
While "radiation" is sometimes used to refer to electromagnetic waves dangerous to humans — such as gamma rays and x-rays — "radiation" can also refer to light, heat, sound, and radio waves.
Radio waves, including all frequencies used by mobile phones, are a form of radiation that can affect human tissue by heating it. This is how microwave ovens work. Mobile phones operate at power levels several orders of magnitude lower than microwave overs, and are therefore incapable of heating human tissue to any measurable degree. There are no other known processes by which radio wave radiation can affect humans.