The Discovery Service is an offloading-related service used by each AEM instance to connect to AEM Topology Connector. The Discovery Service is part of the Sling Discovery framework, which is responsible for detecting and managing the topology of AEM instances. It enables instances to discover each other and establish a clustered topology, which is essential for load-balancing, failover, and other distributed operations.
Option A, "Cluster Service," is not a standard term used in AEM for connecting to the Topology Connector.
Option C, "Topology Connector Service," is a slightly misleading term; the correct term is Discovery Service, which performs the role described.