What characteristic do all proper fractions share?

All proper fractions share the characteristic that the denominator is always greater than the numerator. This definition establishes proper fractions as fractions where the value is less than one. For example, in the fraction 3/4, the denominator (4) is greater than the numerator (3), which signifies that the fraction represents a value that is less than one whole.

In contrast, fractions that have equal numerators and denominators, such as 4/4, equal one, while those with numerators greater than the denominators, such as 5/4, are termed improper fractions, representing values greater than one. Therefore, the defining feature of proper fractions—as characterized by the relationship between the numerator and denominator—is that the numerator is a smaller integer than the denominator.