Linux General Question:

scp- copying files using ssh(secure copy) of the selected files from the source host to destination host and when finished closes the scp application

rsync- you need to setup the key authentication between the
servers that do the synchronization (to destinatio system to have the source public key in destination host's authorized_keys) and copies the files from source to destination whenever there is a change(addition/deletion) in the sounce directory .. can be pull/push/both