Constant
A constant is a symbol employed as an unambiguous name — distinguished from a variable (q.v.).
Thus in ordinary numerical algebra and in real number theory, the symbols x, y, z are variables, while 0, 1, 3, — 1/2, p, e are constants. In such mathematical contexts the term constant is often restricted to unambiguous (non-variable) names of numbeis. But such symbols as +, =, < may also be called constants, as denoting particular functions and relations.
In various mathematical contexts, the term constant will be found applied to letters which should properly be called variables (according to our account here), but which are thought of as constant relatively to other variables appearing. The actual distinction in such cases, as revealed by logistic formalization, either is between free and bound variables, or concerns the order and manner in which the variables are bound by quantifiers, abstraction operators, etc.
In mathematics, the word constant may also be employed to mean simply a number (“Eulers constant”), or, in the physical sciences, to mean a physical quantity (“the gravitational constant,” “Planck’s constant”). — A.C.