wave number

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The number of waves per unit distance in a series of waves of a given wavelength; the reciprocal of the wavelength.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The number of waves per unit length; the reciprocal of wavelength.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the reciprocal of the wavelength of a wave