Cardinal numbers are best defined as:

Cardinal numbers are best defined as numbers that indicate quantity. They are used to count objects and answer the question "how many?" For example, when you have three apples, the number three is a cardinal number because it expresses the quantity of apples present.

In contrast, options that mention ordering items refer to ordinal numbers, which define the position or order of items, such as first, second, or third. Mathematical operations involve the use of various types of numbers, including cardinal numbers, but the term does not specifically denote cardinality, as it reflects actions like addition, subtraction, multiplication, or division. Lastly, while zero is considered in the context of cardinal numbers to indicate the absence of quantity, the broader definition does not limit cardinal numbers to those including zero; cardinal numbers also encompass all positive integers and thereby illustrate quantities larger than zero. Thus, defining cardinal numbers primarily focuses on their role in quantifying rather than ordering or operation.