1. Physics.the point at which a substance in one phase, as the liquid, has the same density, pressure, and temperature as in another phase, as the gaseous.
a. (of a function of a single variable) a point at which the derivative of the function is zero.
b. (of a function of several variables) a point at which all partial derivatives of the function are zero.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.