What is the smallest item of information in a transaction set called?

The smallest item of information in a transaction set is referred to as an element. In the context of data structures and transaction sets, an element is a fundamental building block that holds a single piece of data. Each element can contain specific information necessary for the transaction to be processed, such as a value or a code that represents a particular entity or action.

Elements are typically grouped together within larger structures, like segments or transaction sets, but they retain their identity as discrete units of information. Understanding elements is fundamental in electronic data interchange (EDI) and similar contexts, where precise data representation is crucial for effective communication and processing.

While terms like "field," "attribute," and "tag" are related to data representation, they have different meanings or contexts that do not specifically denote the smallest unit of information as described in this scenario. In summary, the term "element" precisely identifies the smallest item of information, making it the correct answer.