# parameter

## English

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### Etymology

From French paramètre, from New Latin parametrum (parameter), from Ancient Greek παρά (pará, beside) + μέτρον (métron, measure).

### Noun

parameter (plural parameters)

1. () A variable kept constant during an experiment, calculation or similar.
2. (programming) An input variable of a procedure definition, that gets an actual value (argument) at execution time (formal parameter).
Roughly, a tuple of arguments could be thought of as a vector, whereas a tuple of parameters could be thought of as a covector (i.e., linear functional). When a function is called, a parameter tuple becomes "bound" to an argument tuple, allowing the function instance itself to be computed to yield a return value. This would be roughly analogous to applying a covector to a vector (by taking their dot product (or, rather, matrix-product of row vector and column vector)) to obtain a scalar.
3. (programming) An actual value given to such a formal parameter (argument or actual parameter).
4. A characteristic or feature that distinguishes something from others.
5. (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.
The parameter of the principal axis of a conic section is called the latus rectum.
6. (crystallography) The ratio of the three crystallographic axes which determines the position of any plane.
7. (crystallography) The fundamental axial ratio for a given species.

#### Usage notes

• (the value used to instantiate the name): Some authors regard use of parameter to mean argument as imprecise, preferring that parameter refers only to the name that will be instantiated, and argument to refer to the value that will be supplied to it at runtime.

#### Translations

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