An
abbreviation for Bohr Sommerfeld (quantization), which states that for a bound quantum state, the action of its classical equivalent is quantized. An improved version of this method is known as EBK quantization, which includes the phase jump
corrections at the classical turning points (the simplest correction is the 1D case, where a factor of 1/2 appears as a result of applying
continuity and differentiability near classical turning points).