noun
wavelength
Used in physics and engineering for the wavelength of light, sound, radio waves, etc. Also used metaphorically for compatibility or being on the same wavelength.
このレーザーの波長は532ナノメートルです。
The wavelength of this laser is 532 nanometers.
彼とはどうも波長が合わない。
I just can't seem to get on the same wavelength with him.
周波数 means 'frequency' (number of cycles per second), while 波長 means 'wavelength' (distance between wave peaks). They are inversely related.
Compound of 波 (wave) and 長 (length), directly corresponding to the concept of wavelength.