The Free On-line Dictionary of Computing (30 December 2018):

fixed point fixpointThe 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)