The Lorentz factor or Lorentz term is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while that object is moving. Wikipedia

Doppler effect Wikipedia Disambiguation

Important factor in special relativity Wikidata

A factor arising frequently in special relativity, to calculate the degree of time dilation, length contraction and relativistic mass of an object moving relative to an observer, defined as ( 1 − v 2 / c 2 ) − 0.5 , where v and c are relative velocity and the speed of light, respectively. Wiktionary

Lorentz factor. Wiktionary (translation)