Each colour has its own particular wavelength and frequency. Each colour can be measured in units of cycles or waves per second.
If we can imagine light traveling in waves like that in an ocean, it is these waves that have the properties of wavelength and frequency. A wavelength is the distance between the same locations on adjacent waves. As an example; an ocean full of waves, that were 10 meters apart, could be said as, having a wavelength of 10, whereas an ocean of waves that were 30 meters apart would be said as having a wavelength of 30.
The same applies to light. The colour RED has a wavelength of around 700 nanometers long - one wave spans only 7 ten millionths of a meter! Whereas, Violet has a much shorter wavelength, so each violet wave would span a much shorter distance.