message is a built-in function in `C source code'.

(message FORMAT-STRING &rest ARGS)

Display a message at the bottom of the screen.
The message also goes into the `*Messages*' buffer, if `message-log-max'
is non-nil. (In keyboard macros, that's all it does.)
Return the message.

In batch mode, the message is printed to the standard error stream,
followed by a newline.

The first argument is a format control string, and the rest are data
to be formatted under control of the string. See `format' for details.

Note: Use (message "%s" VALUE) to print the value of expressions and
variables to avoid accidentally interpreting `%' as format specifiers.

If the first argument is nil or the empty string, the function clears
any existing message; this lets the minibuffer contents show. See
also `current-message'.