Rational Expressions
An algebraic expression, which can be expressed in the from P/Q, where P and Q (non-zero polynomials) are polynomials, is called a rational expression.
A rational expression need not be a polynomial. On the contrary, every polynomial is also a rational expression.
Examples:
$$ \frac{x + 1}{x - 1} $$
$$ \frac{x^2 - 3x + 5}{x^2 - 5} $$
$$ \frac{4x^2 + 6x - 10}{1} $$