a. The term "rational" in "rational number" and "rational expression" refers to the ability to express the number or expression as a quotient of integers or polynomials, respectively.
b. A rational expression will often have at least one non-permissible value, such as in the expression \(\frac{x+1}{x-2}\), where \(x = 2\) is non-permissible.
\(\boxed{\text{a. Rational refers to quotients; b. Example: } \frac{x+1}{x-2}, x \neq 2}\)