What term describes a part or item forming a piece of a whole?

The term that accurately describes a part or item that forms a piece of a whole is a fraction. A fraction represents a value that is part of a whole, expressed with a numerator and a denominator. For example, in the fraction 3/4, the numerator (3) indicates how many parts we have, while the denominator (4) indicates how many total parts make up the whole. This concept is fundamental in mathematics as it allows for the representation and calculation of parts of quantities and is frequently used in various applications ranging from basic arithmetic to advanced mathematics.

In contrast, a ratio is a comparative relationship between two numbers, while a sum refers to the result of adding numbers together. A whole number, on the other hand, is an integer that does not include fractions or decimals and is considered complete in itself. Therefore, among the choices provided, a fraction is the most fitting term for describing a part of a whole.