TELNET is an abbreviation for TErminaLNETwork. TELNET is a general-purpose client-server application program.

SSH (Secure Shell) is another popular remote login application program, like TELNET, uses TCP as the underlying transport protocol, but SSH is more secure and provides more services than TELNET.

SSH is preferred over telnet because of security issues, telnet doesn't use any encryption therefore the information is transmitted in a form of plain text even the password.

Whereas, SSH use encryption to encryptthe information and assures confidentiality and integrity of data by using PKI model (public key infrastructure).