You create a service in MDG config first. Then, you use that name in the BRF+ application. When you implement the BAdI, you use that service name as a filter so the application knows to call which BAdI implementation for that specific BRF+ application.
See this document (search for the team "service name"): How to-Master Data Governance for Material: BADI USMD_SSW_RULE_CONTEXT_PREPARE to Enhance User Determination.