What is the purpose of "rsync" and what makes it efficient for synchronizing files?

A "rsync" synchronizes files between locations, locally or over a network, using a delta-transfer algorithm that sends only the differences between source and destination, making repeated syncs of large files much faster than a full copy B "rsync" always copies entire files regardless of what has changed, just like "cp" C "rsync" can only be used between two directories on the same local machine D "rsync" permanently deletes the source files after copying