Complex sentence: The term C-number is an old nomenclature used by Paul Dirac to distinguish between real or complex numbers (c-numbers or classical numbers) and operators (q-numbers or quantum numbers) in quantum mechanics.
Split into simpler sentences: The term c-number (or classical number) is an old nomenclature used by Paul Dirac, and it refers to real and complex numbers. It is used to distinguish from operators (q-numbers or quantum numbers) in quantum mechanics.