Definition of parameter
1 a : an arbitrary constant whose value characterizes a member of a system (as a family of curves); also : a quantity (as a mean or variance) that describes a statistical population b : an independent variable used to express the coordinates of a variable point and functions of them — compare parametric equation
2 : any of a set of physical properties whose values determine the characteristics or behavior of something <parameters of the atmosphere such as temperature, pressure, and density>
3 : something represented by a parameter : a characteristic element; broadly : characteristic, element, factor <political dissent as a parameter of modern life>
4 : limit, boundary —usually used in plural <the parameters of science fiction>
parameter vs. perimeter
It's very easy to confuse parameter with perimeter. Not only do the two words sound the same, they both connote a boundary or limit.
When parameter is used to mean "a boundary or limit," it is usually in its plural form, and often as the object of a preposition such as within or beyond:
Let's face it, managing weight loss or maintenance can be trying enough within the parameters of a daily routine.
Geoff Kerr, Weight Watchers, November 1991Though candor sometimes encourages Bruno to "stray beyond the parameters of good taste," his interaction with Lydia is always convincingly portrayed as a loving, tender relationship.
Ron Charles, The Washington Post, 8 Feb. 2011
In geometry, perimeter refers to the boundary of a closed plane figure. You might remember calculating perimeters in school. If each side of an equilateral triangle measures 9 feet, then the perimeter of the triangle measures 27 feet. In more general use, perimeter describes an outer stretch, as in "The college president lived in a house on the perimeter of the campus."
Parameter originally had a meaning pertaining to mathematics as well. The dictionary defines it as "an arbitrary constant whose value characterizes a member of a system (as a family of curves); also : a quantity (as a mean or variance) that describes a statistical population" as well as "an independent variable used to express the coordinates of a variable point and functions of them."
Some twentiethcentury usage commentators objected to the use of a scientificsounding word like parameter in general contexts (as in the examples above), especially to mean "a limit or boundary," theorizing that perimeter must have been what the speaker or writer intended.
However, perimeter was not often used in the phrasings that parameter is used in (that is, as the object of within or beyond) until much later. In fact, a word such as bounds or range or confines often serves as a more appropriate equivalent for parameter than the marginal connotations of perimeter:
But a true novel is an extended piece of fiction: Length is clearly one of its parameters.
Anthony Burgess, The New York Times Book Review, 5 Feb. 1984Shields will then subsume that request in the overall City operating budget that he will recommend to the City Council in midMarch, and the Council will make its final decisions on the parameters of the budget, including any tax increases or cuts, by the end of April.
Nicholas F. Benton, The Falls Church News Press, 6 Jan. 2016
Origin and Etymology of parameter
New Latin, from para + Greek metron measure — more at measure
First Known Use: 1852
Other Mathematics and Statistics Terms
PARAMETER Defined for English Language Learners
parameter
playDefinition of parameter for English Language Learners

: a rule or limit that controls what something is or how something should be done
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Spanish Central: Translation of parameter Nglish: Translation of parameter for Spanish speakers Britannica English: Translation of parameter for Arabic speakers Britannica.com: Encyclopedia article about parameter
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