The quantity that is "waving" is the electromagnetic field, an esoteric but quite measurable entity: your lights shine and your microwave runs and your radio plays because the electromagnetic field exists. Here is a Java applet illustrating wave motion in the electric and magnetic fields.

Units of Wavelength
Unit	Symbol	Length
centimeter	cm	10-2 meters
Angstrom		10-8 centimeters
nanometer	nm	10-9 meters
micrometer	nm	10-6 meters

As illustrated in the adjacent image, a wave has a wavelength associated with it. It is normal to give the wavelength of light the symbol Greek "lambda". Some common units of length employed for wavelengths of electromagnetic radiation are summarized in the adjacent table. (The micrometer is often still called by its old name, the micron.)

The speed of light in a vacuum is commonly given the symbol c. It is a universal constant that has the value