noun

- Mathematics.
- a constant or variable term in a function that determines the specific form of the function but not its general nature, as a in f(x) = ax, where a determines only the slope of the line described by f(x).
- one of the independent variables in a set of parametric equations.

- Statistics. a variable entering into the mathematical form of any distribution such that the possible values of the variable correspond to different distributions.
- Computers. a variable that must be given a specific value during the execution of a program or of a procedure within a program.
- Usually parameters. limits or boundaries; guidelines: the basic parameters of our foreign policy.
- characteristic or factor; aspect; element: a useful parameter for judging long-term success.

noun

- one of a number of auxiliary variables in terms of which all the variables in an implicit functional relationship can be explicitly expressedSee parametric equations
- a variable whose behaviour is not being considered and which may for present purposes be regarded as a constant, as y in the partial derivative ∂f(x,y)/∂ x
- statistics a characteristic of the distribution of a population, such as its mean, as distinct from that of a sampleCompare statistic
- informal any constant or limiting factora designer must work within the parameters of budget and practicality

n.1650s in geometry, from Modern Latin parameter (1630s), from Greek para- “beside, subsidiary” (see para- (1)) + metron “measure” (see meter (n.2)). A geometry term until 1920s when it yielded sense of “measurable factor which helps to define a particular system” (1927). Common modern meaning (influenced by perimeter) of “boundary, limit, characteristic factor” is from 1950s. Related: Parametric. n.

- One of a set of measurable factors, such as temperature and pressure, that define a system and determine its behavior and are varied in an experiment.
- A factor that determines a range of variations; a boundary.
- A statistical quantity, such as a mean or standard deviation of a total population, that is calculated from data and describes a characteristic of the population as opposed to a sample from the population.
- A psychoanalytic tactic, other than interpretation, used by the analyst to further the patient’s progress.
- A factor that restricts what is possible or what results. Not in technical use.
- A distinguishing characteristic or feature. Not in technical use.

A quantity or number on which some other quantity or number depends. An informal example is, “Depending on the traffic, it takes me between twenty minutes and an hour to drive to work”; here, “traffic” is the parameter that determines the time it takes to get to work. In statistics, a parameter is an unknown characteristic of a population — for example, the number of women in a particular precinct who will vote Democratic.