SCP means a Secure Copy. It is a method of remote communication and sending files between networks where the sent files are secured with the SSH (Security Shell) protocol. It allows transferring files without information leaks. SCP is a substitute for the legacy `cp` file transfer application.
SFTP stands for Secure File Transfer Protocol. This is an application which uses Secure Shell in relocating files. It avoids the plain transmission of data and it does not only protect the information, but also encrypts the commands. SFTP is a substitute for the `ftp` - file transfer protocol.