A proper fraction is defined as a fraction where the numerator (the top number) is less than the denominator (the bottom number). For example, if we consider the fractions 1/2, 3/4, and 5/3, the fractions 1/2 and 3/4 are proper fractions because in both cases, the numerators (1 and 3) are less than the denominators (2 and 4). On the other hand, 5/3 is not a proper fraction because the numerator (5) is greater than the denominator (3).
So, among a list of fractions, any fraction where the numerator is less than the denominator would be classified as a proper fraction. Always remember this simple rule when identifying proper fractions.