ETYM Latin onstans, -antis, p. pr. of constare to stand firm, to be consistent; con- + stare to stand: cf. French constant. Related to Stand and cf. Cost.
1. Continually recurring or continuing without interruption.
2. Steadfast in purpose or devotion or affection.

In mathematics, a fixed quantity or one that does not change its value in relation to variables. For example, in the algebraic expression y2 = 5x - 3, the numbers 3 and 5 are constants. In physics, certain quantities are regarded as universal constants, such as the speed of light in a vacuum.
A named item that retains a consistent value throughout the execution of a program, as opposed to a variable, which can have its value changed during execution. Compare variable.