A numerical address for postal correspondence, managed by a company or organisation on behalf of the addressee, and used e.g. for convenience, if one does not have a suitable physical address for receiving mail, or to avoid giving one's real address (e.g. in a newspaper advertisement).

(idiomatic) Alternative form of look out for number one

plural of all-figure number

(UK, telecommunications, historical) A telephone number consisting purely of digits, introduced in the 1960s to replace numbers that began with an alphabetic code for the exchange.

(theater) A showstopping song that occurs late in the second act of a two-act musical, often signifying a moment of revelation or change of heart of a lead character.

plural of 11 o'clock number

plural of Fresnel number

(optics) A dimensionless quantity (denoted F), such that for an electromagnetic wave passing through an aperture and hitting a screen, F=(a²)/(L𝜆) where a is the characteristic size (e.g. radius) of the aperture, L is the distance of the screen from the aperture, and 𝜆 is the incident wavelength.

(mathematics, number theory) The field of study dealing with computational methods for investigating and solving problems in number theory and arithmetic geometry.

Of or relating to the ancient Celtiberian city of Numantia.