Reference data is data that defines the set of permissible values to be used by other data fields. Reference data gains in value when it is widely re-used and widely referenced. Typically, it does not change overly much in terms of definition (apart from occasional revisions). Reference data often is defined by standards organizations (such as country codes as defined in ISO 3166-1). Typical examples of reference data are:

• Units of measure
• Country codes
• Corporate codes
• Fixed conversion rates (e.g., weight, temperature, and length)
• Calendar (structure and constraints)

Reference data should be distinguished from master data, which represents key business entities such as customers and materials in all the necessary detail (e.g., for customers: number, name, address, and date of account creation). In contrast, reference data usually consists only of a list of permissible values and attached textual descriptions. A further difference between reference data and master data is that a change to the reference data values may require an associated change in business process to support the change; a change in master data will always be managed as part of existing business processes. For example, adding a new customer or sales product is part of the standard business process. However, adding a new product classification (e.g. restricted sales item) or a new customer type (e.g. gold level customer) will result in a modification to the business processes to manage those items.