everybody lately is talking about TUIs. what do these people mean?

(I trace my adult involvement with computers back to (a) terminals and (b) where you didn't know if your terminal and terminal driver would support ANSI cursor positioning (stty raw!) so I feel equipped to understand what people are talking about, I just don't know.)

is emacs a tui? is midnight commander a tui? vi? I assume the cli is not a tui? are we not even talking about terminals?