What term describes a number that cannot be expressed as a fraction?

The term that describes a number that cannot be expressed as a fraction is "irrational." Irrational numbers are those that cannot be written in the form of a fraction where both the numerator and the denominator are integers. Instead, these numbers have non-repeating, non-terminating decimal expansions. Examples of irrational numbers include √2, π, and e.

In contrast, integers are whole numbers that can be positive, negative, or zero. Rational numbers can be expressed as a fraction and include integers, whole numbers, and any number that can be represented in fractional form. Whole numbers are a subset of integers that include all non-negative integers (0, 1, 2, 3, ...).

Thus, the distinguishing feature of irrational numbers is their inability to be represented as simple fractions, which is why this term correctly identifies numbers of that nature.