In a nutshell, there are three types of program interfaces. CLI, TUI, and GUI. GUI means it is graphical, buttons, menus, that sort of thing. CLI and TUI both rely the terminal (they are “non-GUI” I guess), where CLI means command line interface, things like “cd” or “tar” would fit into this. TUI means terminal user interface, and they usually involve keyboard navigation, but you still have menus and such. A good example I use a lot is rmpc, a neat music player! There are some TUI programs that also support mouse input, like aforementioned rmpc, but it’s not the focus.

TLDR: GUIs have buttons you click with a mouse, TUIs have menus that can be navigated via a keyboard, CLIs mean you type commands into the terminal.