From LQWiki

When you run a command line program, usually it's the sort where lines of text scroll up the screen, perhaps stopping for you to enter some input -- all on a line-by-line basis. These sorts of programs are said to have a command line interface. You run them from a terminal or terminal window.

Other terminal programs present to you a sort of text-based text-only GUI that takes place right there in the terminal. Programs like vim and lynx do this. When run, these programs take over the terminal's display, and use all width x height elements to create a sort of textual blocky GUI. Usually, this feat is accomplished using the ncurses library.

Ncurses-based programs tend to be fairly easy to use, and very fast.