Connections
Serial, Telnet and local shell
Other kinds of tab that behave like an SSH session.
A terminal tab does not have to be SSH. These sessions use the same terminal.
Serial
A serial tab opens a port with the line settings you choose, and lists the ports the machine has. For devices that move files with XMODEM or YMODEM, see ZMODEM, XMODEM and YMODEM.
Telnet
For devices that offer nothing else. The client negotiates the options a terminal needs: remote echo, suppress go-ahead, terminal type, window size and binary.
Telnet is not encrypted and has no authentication of its own. Everything you type travels in the clear.
Local shell
Runs your login shell on a pseudo-terminal of this machine: a pty on macOS and Linux, ConPTY on Windows.