Wiktionary
n. (context mathematics English) Any function whose value can be expressed as the quotient of two polynomials (except division by zero)
Wikipedia
In mathematics, a rational function is any function which can be defined by a rational fraction, i.e. an algebraic fraction such that both the numerator and the denominator are polynomials. The coefficients of the polynomials need not be rational numbers, they may be taken in any field K. In this case, one speaks of a rational function and a rational fraction over K. The values of the variables may be taken in any field L containing K. Then the domain of the function is the set of the values of the variables for which the denominator is not zero and the codomain is L.
The set of rational functions over a field K is a field, the field of fractions of the ring of the polynomial functions over K.
Usage examples of "rational function".
The drink shocked him, revived him, lifted him another notch toward rational function.
The rational function of his mind grew at the expense of the imaginal.