The concept of tracking the number of MDM subject areas and source system attributes Is referred to as:

Tracking the number of MDM subject areas and source system attributes refers to defining the scope

and coverage of the subject areas and attributes involved in an MDM initiative. This process includes

identifying all the data entities (subject areas) and the specific attributes (data elements) within

those entities that need to be managed across the organization. By establishing a clear scope and

coverage, organizations can ensure that all relevant data is accounted for and appropriately

managed.

Reference:

DAMA-DMBOK2 Guide: Chapter 10 – Master and Reference Data Management

"Master Data Management and Data Governance" by Alex Berson, Larry Dubov