A fundamental assumption, a self-evident principle. In deductive scientific theories the axioms are the fundamental primitive assumptions of the given theory from which its remaining contents is derived by deduction, i.e. by purely logical procedures. Cf. Axiomatic method.
Axiom. P.S. Novikov (originator), Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Axiom&oldid=16486