Which of these best describes invalid data?

The best description of invalid data is that it does not conform to validation rules. Validation rules are criteria set to ensure that the data meets specific standards or expectations regarding format, type, range, or accuracy. When data fails to adhere to these predefined rules, it is considered invalid. This can occur due to various reasons, such as incorrect data entry, missing values, out-of-range entries, or incompatible formats.

For example, if a validation rule specifies that a date must be formatted as 'YYYY-MM-DD' and an entry is provided as 'MM/DD/YYYY', it does not conform to the rules and is therefore invalid. Thus, the emphasis on validation rules provides a clear criterion for determining the legitimacy of data, making this option the most accurate definition of invalid data.