As we know that wave is the periodical disturbance which is travelled through medium from particle to particle and if we observe the movement of wave then the phase is changed with time. There’s some important terms related to wave like frequency, wavelength, wave number, velocity of wave etc. Two most important parts of waves are crest and trough by which it is travelled from one part to other part. The upper part is called the crest while the lower part is called trough. The height of each crest is same to the deepness of each trough. One crest is followed by second and second follows the next one. This process is similar for trough. Wavelength is defined as the distance between two nearest points of the adjacent c crest or trough. This is the distance between the wave cycles which are propagated in space. It is a length therefore it is measured in terms of units of length like meters or centimeters or millimeters or Nano-meters (10-9meter) or Angstrom units (10-10 meter). Therefore we discuss now about wavelength and it is mathematical representation or formula, and how one term is calculated by using the knowing value of other terms . .