A secure copy protocol.
Copy file like cp command, but over differnt host from {host1}'s {path1} to {host2}'s {path2}
scp -P 22 {user1}@{host1}:{path1} {user2}@{host2}:{path2}
If the director is localhost, you could omit the ssh access {user}@{host}:. e.g. scp file.txt {user1}@{host1}:{director on host1}
If the server use standard ssh port (port 22), the argument -P 22 can be omited.