In mathematical physics, the WKB approximation or WKB method is a method for finding approximate solutions to linear partial differential equations with spatially varying coefficients. It is typically used for a semiclassical calculation in quantum mechanics in which the wavefunction is recast as an exponential function, semiclassically expanded, and then either the amplitude or the phase is taken to be slowly changing.
The name is an acronym for Wentzel–Kramers–Brillouin. It is also known as the LG or Liouville–Green method. Other often-used acronyms for the method include JWKB and WKBJ, where the "J" stands for Jeffreys.
Read more about WKB Approximation: Brief History, WKB Method, An Example, Application To Schrödinger Equation