As Chemists we often generalize all electromagnetic radiation as "light". While often we are talking about visible light, we can also lump in UV or infrared radiation or even x-rays or radio waves. All of these are electromagnetic radiation: a traveling wave characterized by an oscillating electric and magnetic fields.
These waves are characterized by three inter-related parameters: wavelength, frequency, and speed. Since the speed of light in a vacuum is a constant, wavelength and frequency end up as two different ways to convey the same information. Therefore EM radiation can be either described by its wavelength or by its frequency but these are completely interchangeable.