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I am trying to clarify my understanding of terminal here.
Terminal is actually a device (keyboard+monitor). When in CLI mode, the input from your keyboard goes directly to shell and also displayed on monitor.
Meanwhile, when using GUI mode, you have to open terminal emulator program to interact with shell. The input from your keyboard goes to terminal emulator program and also displayed on terminal emulator window on monitor. The input does not directly goes to shell. The terminal emulator program will relay the input from your keyboard to shell. The terminal emulator program communicates with the shell using pseudo-terminal.
There is no terminal emulator program involved when you go straight to CLI from boot.
Please comment and correct me if anything wrong with my understanding.
Update: I read back TTY demystified. I think what I should ask is the difference between text terminal (boot straight to text mode) and GUI terminal because I thought terminal=text terminal, terminal emulator=GUI terminal e.g. Gnome Terminal, which are wrong. From the answers in regards to before this update, a user is actually using terminal emulator program (user space) too like in GUI mode. May I know is it TTY program because I found TTY process when running command 'ps aux'. I never knew there is terminal emulator program involved too (not referring to terminal emulator in kernel space) in text mode.
Update2: I read Linux console. According to it, text mode is console, meanwhile terminal software in GUI mode is terminal emulator. Well, it makes sense and it is same with my understanding before. However, according diagram from TTY demystified, terminal emulator is in the kernel space instead of user space. Interestingly, the diagram refers to text mode.