Master data and reference data are two types of data that are shared enterprise wide and even in the wider business ecosystem where your company operates.
In your organization and business ecosystem the data that is shared is basically held in applications like ERP and CRM solutions that have come with a data model provided by the solution vendor. These data models are built to facilitate the operations that is supported by each of these applications and is a data model that must suite every kind of organization.
A core reason of being for a Master Data Management (MDM) solution is to provide a data store where master data is represented in a way that reflects the business model of your organization. This data store serves many purposes as for example being a data integration hub and the place where the results of data quality improvements (eg de-duplication) are stored.
Such a data hub can go beyond master data entities and represent reference data and critical application data that is shared across your organization and the wider business ecosystem within a given industry.
Learn more about flexible data models in a data hub context in the Semarchy whitepaper authored by me and titled The Intelligent Data Hub: Taking MDM to the Next Level.
Liliendahl on Data Quality 