telnet was widely used for remote terminal access, but it sends credentials and session data without encryption. It should not be used for administrative logins on modern networks.
Use SSH for remote login
ssh user@serverSSH encrypts authentication and session traffic and is the normal replacement for Telnet remote access.
Where telnet can still appear
The Telnet client is sometimes used to make a simple TCP connection to a service for testing, but tools such as nc, curl, openssl s_client, or protocol-specific clients are usually better choices.
This page is retained as a legacy networking note. Do not enable a Telnet server simply to follow an old tutorial.