The exponents must be non-negative integers.
Examples:
[tex]x[/tex] is a polynomial (degree 1)
[tex]x^2-1[/tex] is a polynomial (degree 2)
[tex]x^3-\dfrac1{x^3}=x^3-x^{-3}[/tex] is NOT a polynomial, but a rational expression
[tex]\sqrt x=x^{1/2}[/tex] is NOT a polynomial, but an algebraic expression.
