A point 
at which the derivative of a function 
vanishes,
A stationary point may be a minimum, maximum, or inflection point.
See also
Critical Point, Derivative, Extremum, First Derivative Test, Inflection Point, Maximum, Minimum, Second Derivative Test
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Cite this as:
Weisstein, Eric W. "Stationary Point." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/StationaryPoint.html