ApplicationConfig.java

@PropertySource("classpath:/com/myco/app.properties")
@Configuration
public class ApplicationConfig {
  
   @Autowired
  Environment env;
  
  //...
  
   @Bean 
   public LocalContainerEntityManagerFactoryBean entityManagerFactory(){
     //Configure the vendor adapter
     HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
     vendorAdapter.setDatabasePlatform(env.getProperty("database.dialect"));
     
     //Create the factory bean
     LocalContainerEntityManagerFactoryBean factoryBean = new LocalContainerEntityManagerFactoryBean();
     factoryBean.setPersistenceUnitManager(pum());
     factoryBean.setJpaVendorAdapter(vendorAdapter);
     
     Map<String, Object> multitenancyMap = new HashMap<String, Object>();
     multitenancyMap.put("hibernate.multi_tenant_connection_provider", multitenancyConnectionProvider());
     multitenancyMap.put("hibernate.tenant_identifier_resolver", tenantResolver());
     multitenancyMap.put("hibernate.multiTenancy", "DATABASE");

     factoryBean.setJpaPropertyMap(multitenancyMap);
      
   }
  
  @Bean
  public MultiTenantConnectionProviderImpl multitenancyConnectionProvider(){
   return new MultiTenantConnectionProviderImpl(); 
  }
    
  @Bean
  public CurrentTenantIdentifierResolverImpl tenantResolver(){
    return new CurrentTenantIdentifierResolverImpl(); 
  }
  //...
}

what is the definition of pum()?