(physics) A measure of the permittivity of a material relative to that of a vacuum.

(mathematics) The constant 1.303577269034..., an algebraic number of degree 71, related to the limit of the growth of the look-and-say sequence.

(computing theory) A real number that informally represents the probability that a randomly-constructed program will halt.

(logic) One of a set of letters or symbols which are assigned fixed truth values independently of any interpretation or valuation, and each of which qualifies as a prime formula of their language.

(mathematics) The problem of deciding whether a given expression is equal to zero.

(programming) An identifier that is substituted by a pre-defined value prior to compilation.

(mathematics) The transcendental number e^(𝜋√), an almost integer, discovered in 1859 by mathematician Charles Hermite.

(electrodynamics) The fundamental physical value α, presumed to be constant, that characterizes the strength of the electromagnetic force.

(airplanes) Something that aims at ensuring that the electric generator produces a constant frequency.

Alternative form of fine-structure constant