CLI refers to interacting with a program by typing commands. Commands need not come from a terminal (a terminal need not even exist). They might be just passed

CLI refers to interacting with a program by typing commands. Commands need not come from a terminal (a terminal need not even exist). They might be just passed in from a different program. TUI refers to interacting with a program via the terminal—the terminal is the program's user interface (think 'nano', which you can't really run without a terminal). The terminal need not interact via commands, although many TUI programs also accept commands.