Source : Webster's Revised Unabridged Dictionary (1913)

Parameter \Pa*ram"e*ter\, n. [Pref. para- + -meter: cf. F.
   param[`e]tre.]
   1.
      (a) (Math.) 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. --Brande & C.
      (b) 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.

   Note: The parameter of the principal axis of a conic section
         is called the latus rectum.

   2. (Crystallog.) The ratio of the three crystallographic axes
      which determines the position of any plane; also, the
      fundamental axial ratio for a given species.

Source : WordNet®

parameter
     n 1: a constant in the equation of a curve that can be varied to
          yield a family of similar curves [syn: {parametric
          quantity}]
     2: any factor that defines a system and determines (or limits)
        its performance
     3: a quantity (such as the mean or variance) that characterizes
        a statistical population and that can be estimated by
        calculations from sample data

Source : Free On-Line Dictionary of Computing

parameter
     
        {formal argument}