rcp stands for the Unix 'remote copy' command. It is a command on the Unix-like operating systems that is used to remotely copy—to copy one or more files from one computer system to another. It uses rlogin for data transfer and uses the same mechanisms for authentication as rlogin.
As described in the rlogin article, rcp is not secure for network use, because it sends unencrypted information over the network, among other things. It has largely been replaced by the ssh-based utility scp.