What's the bar below the mode-line?

I would like to remove that bar locally to specific buffers (i want essentially just text with syntax highlighting), but I don't know what it's called: the bar where evaluating (+ 1 2) would print 3 or show Auto-saving... done, from time to time.

That area can show either of two entities: when entering input it shows the “minibuffer”; when displaying results it shows the “echo area”. These are two distinct concepts which appear in the same physical space.

It is the echo area