Website host addressThis is the address where the website replications should be received from. The address to use is the one found on the site in the field Address (found when selecting properties for the website and selecting Website properties).
Shared security keyInformation the source server must use. This is created on the source server.
Read onlyCheck this box if the replicated (received) website should be read only. The only user that can do more than just read if you check this box is the system user. In other words - this is a convenient way of ensuring that normal users are not allowed to edit or alter pages that are received (replicated) from another server (changes on the pages have to be done on the source server).
If you want to remove a replication source, select it in the list and click the minus icon. If you would like to change a replication source, click the properties button.