In mathematics, statistics, and the mathematical sciences, a parameter (G: auxiliary measure) is a quantity that serves to relate functions and variables using a common variable (often t) when such a relationship would be difficult to explicate with an equation
f(x) = ax2 + bx + c;
here the variable x designates the function argument, but a, b, and c are parameters that determine which quadratic function one is considering.
字源：1656, from Mod.L. parameter (1631), from Gk. para- "beside, subsidiary" + metron "measure" . A geometry term until 1920s when it yielded sense of "measurable factor which helps to define a particular system" (1927).