(physics) any of a set of physical quantities that play a fundamental role in basic theories

(physics) a universal constant, R, that appears in the ideal gas law, PV=nRT, derived from two fundamental constants, the Boltzmann constant and Avogadro's number, R=N_Ak.

Alternative spelling of Hubble constant

(astronomy) A number that expresses the rate of expansion of the universe; the velocity at which a distant object is receding from the Earth divided by its distance; its reciprocal determines the age of the universe.

(physics) A numerical constant used in determining the electrostatic energy of each ion in a crystal.

(physics) A universal scaling factor for all spectroscopic transitions.

The amount of incoming solar radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays.

(mathematics) A function whose value is the same for all the elements of its domain.

(mathematics) A characteristic of an exponential function, represented by τ in the function:

(calculus) An unspecified constant term added to a particular antiderivative to make it represent its whole family of antiderivatives, usually denoted with C.