Clustering? Replication? Sync? REST APIs
Clustering is where a set of identical alfresco repositories work together as one. To give high availability or greater performance.
Replication is where a subset of data is transferred to a different instance of alfresco.
Sync is where content is transferred in/out of alfresco. Or between alfresco enterprise and alfresco cloud.
REST APIs are a remote interface for alfresco based upon HTTP.