(physics) a reproducible invariant temperature; the boiling point, freezing point, or triple point of a substance, such as water, that is used to calibrate a thermometer or define a temperature scale
2.
(maths) a point that is not moved by a given transformation
mathematics The fixed point of a function, f is any value, x for which f x = x. A function may have any number of fixed points from none (e.g. f x = x+1) to infinitely many (e.g. f x = x). The fixed point combinator, written as either "fix" or "Y" will return the fixed point of a function. See also least fixed point. (1995-04-13)