Which type of numbers can be expressed as a fraction?

Rational numbers are defined as numbers that can be expressed as a fraction, where both the numerator and the denominator are integers, and the denominator is not zero. This definition encompasses a wide variety of numbers, including integers (which can be expressed as a fraction with a denominator of 1) and terminating or repeating decimals.

In contrast, while whole numbers and natural numbers can be included under the umbrella of rational numbers, they are specific subsets and do not fully represent the broader category of numbers that can appear as fractions. Irrational numbers, on the other hand, cannot be expressed as a fraction; they include numbers like the square root of 2 or π, which have non-repeating, non-terminating decimal expansions. Thus, rational numbers are the most accurate answer to this question regarding the type of numbers that can be expressed as a fraction.