Parameter and Variable

noun

• A constant in the equation of a curve that can be varied to yield a family of similar curves.
  • synonyms: parametric quantity
• Any factor that defines a system and determines (or limits) its performance.
• Computer science. ( a reference or value that is passed to a function, procedure, subroutine, command, or program)
  • synonyms: argument
• A quantity (such as the mean or variance) that characterizes a statistical population and that can be estimated by calculations from sample data. .

• (n.) The ratio of the three crystallographic axes which determines the position of any plane; also, the fundamental axial ratio for a given species.
• (n.) Specifically (Conic Sections), 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.
• (n.) A term applied to some characteristic magnitude whose value, invariable as long as one and the same function, curve, surface, etc., is considered, serves to distinguish that function, curve, surface, etc., from others of the same kind or family.

Parameter is a model is a combination of variables, such as GDP growth, and coefficients which multiply these variables. The coefficients are often estimated from the data. The coefficients are called parameters.

noun

• Something that is likely to vary; something that is subject to variation.
  • usage: "the weather is one variable to be considered"
• A quantity that can assume any of a set of values.
  • synonyms: variable quantity
• A star that varies noticeably in brightness.
  • synonyms: variable star
• A symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity.

adjective

• Liable to or capable of change.
  • usage: "rainfall in the tropics is notoriously variable"; "variable winds"; "variable expenses"
• Marked by diversity or difference.
  • usage: "the varying angles of roof slope"; "nature is infinitely variable"
  • synonyms: varying
• Used of a device) designed so that a property (as e. G. Light) can be varied. (
  • usage: "a variable capacitor"; "variable filters in front of the mercury xenon lights"

• (n.) Those parts of the sea where a steady wind is not expected, especially the parts between the trade-wind belts.
• (n.) That which is variable; that which varies or is subject to change.
• (a.) Liable to vary; too susceptible of change; mutable; fickle; unsteady; inconstant; as, the affections of men are variable; passions are variable.
• (n.) A quantity which may increase or decrease; a quantity which admits of an infinite number of values in the same expression; a variable quantity; as, in the equation x2 - y2 = R2, x and y are variables.
• (a.) Having the capacity of varying or changing; capable of alternation in any manner; changeable; as, variable winds or seasons; a variable quantity.
• (n.) A shifting wind or one that varies in force.

Variable is an element in a model. For example, in the model RS&Pt+1 = a + b Tbill t + et, where RS&Pt+1 is the return on the S&P in month t+1 and Tbill is the Tbill return at month t, both RS&P and Tbill are "variables" because they change through time; i. E., they are not constant.