A terminal is just the input+output endpoint you use to talk to a computer — historically a separate physical device, today usually a software window.

The word "terminal" predates computers as we know them. Early mainframes filled a room, and users sat at a terminal: a device with a way to send input and a way to receive output. It "terminates" the line between you and the machine.

The key idea that carries into modern Linux: the terminal is not the computer — it's the access point. That separation is why one server can be reached from many terminals at once, and why "opening a terminal" on your laptop really means opening a program that emulates one of those old devices.

A terminal can be graphical (mouse + windows) or text-based (keyboard + a text grid). When people say "the terminal" in a Linux context, they almost always mean the text one, because that's where the shell lives.