(physics) The numerical extent to which a quantum state is filled (in a system of many, identical quantum particles)

(grammar) Grammatical number denoting a quantity of exactly three

plural of copy number

(astronomy) The total number of stars in the observable universe, often estimated to be in the sextillions.

Any of several forms of fixed-length identification number on stamps, books, etc.

plural of Wratten number

Any of the arbitrary alphanumeric codes in a system for labelling optical filters, usually for photographic use.

plural of silent number

plural of call number

plural of dial number