It is a metaphor in the sense that the name is coming from the TeleType console writer:
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...which was essentially an ancient electromechanical writing machine. It was used as the keyboard of some ancient unix big computer.
Today, the few remaining parts of them are in IT museums. But the console character devices still named as `/dev/tty` or similarly.
Its current meaning is roughly "kernel-driven character console".
Many character environments _don't need_ a tty device for a functioning CLUI (Command Line User Interface), and may work with or without one.