A value kept constant during an experiment, equation, calculation, or similar, but varied over other versions of the experiment, equation, calculation, etc.

(sciences) A variable that describes a system or aspect of a system, often used in statistics and machine learning.

(programming) An input variable of a function definition, that gets an actual value (argument) at execution time.

(programming, loosely) An actual value given to such a formal parameter.

A characteristic or feature that distinguishes something from others.

(geometry) In the ellipse and hyperbola, a third proportional to any diameter and its conjugate, or in the parabola, to any abscissa and the corresponding ordinate.

(crystallography) The ratio of the three crystallographic axes which determines the position of any plane.

(crystallography) The fundamental axial ratio for a given species.