\vfill ¶Synopsis:
\vfill
End the current paragraph and insert a vertical rubber length that is infinite, so it can stretch or shrink as far as needed (see Lengths).
It is often used in the same way as \vspace{\fill}, except that
\vfill ends the current paragraph whereas \vspace{\fill}
adds the infinite vertical space below its line, irrespective of the
paragraph structure. In both cases that space will disappear at a page
boundary; to circumvent this see the starred option
in \vspace.
In this example the page is filled, so the top and bottom lines contain the text ‘Lost Dog!’ and the second ‘Lost Dog!’ is exactly halfway between them.
\begin{document}
Lost Dog!
\vfill
Lost Dog! % perfectly in the middle
\vfill
Lost Dog!
\end{document}