The echo area is used for displaying error messages
(see Errors), for messages made with the message primitive,
and for echoing keystrokes. It is not the same as the minibuffer,
despite the fact that the minibuffer appears (when active) in the same
place on the screen as the echo area. The GNU Emacs Manual
specifies the rules for resolving conflicts between the echo area and
the minibuffer for use of that screen space (see The Minibuffer).
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see Output Functions), or
explicitly.