a data element that is determined to be vital to the successful operation of the organization

For example, an organization may define its critical data elements as those that represent protected personal information, those that are used in financial reports (both internal and external), regulatory reports, the data elements that represent identifying information of master data objects (e.g., customer, vendor, or employee data), the elements that are critical for a decision-making process, or the elements that are used for measuring organizational performance.
Such data elements are a subset of defining metadata.

data element, Factsheet Critical Data Elements, Factsheet Metadata

Loshin, 2009