Meaning of QUANTUM in English

[noun] [C] [plural] quanta [formal] - the smallest amount or unit of esp. energyquantum theoryA quantum leap is a great improvement or important advance in something.The appointment of a female director is a quantum leap for women's equality.(specialized) In physics, quantum mechanics is a theory that explains the behaviour of elementary particles, both separately and in groups.

Cambridge English vocab.      Кембриджский английский словарь.