What is millimeter wave?

As the name suggests, millimeter waves are electromagnetic waves with a wavelength (λ) of about 1 millimeter (more precisely, 1 to 10 millimeters). By using the formula f = c/λ, where c is the speed of light (3E8 m/s), the wavelength can be converted into a frequency range of 30-300 GHz. The millimeter wave frequency band has been designated as the "extremely high frequency" (EHF) band by the International Telecommunication Union (ITU). The term "millimeter wave" is also commonly abbreviated as "mmWave".