Customer Master Data Management — Maintains one canonical customer record — legal entities, hierarchies, addresses, tax IDs — across every revenue system. Everything downstream keys off it: invoicing pulls bill-to entities, tax calculation pulls registrations, and consolidation pulls the account hierarchy.
Customer Master Data Management lives in the Fulfill & Activate phase of Fulfill & Bill — the stage where you activate what was sold, meter what's used, bill it right. In the corpus tool index this phase maps to the Entitlements and Billingcategories.