The question of how to use a font size smaller than "tiny" in LaTeX is not as straightforward as it seems, as it also depends on the chosen font.
With the default font, it's not possible to use a font size smaller than "tiny" because the standard font does not support all sizes. To address this limitation, it's recommended to include the lmodern package. Once this is done, you can use commands like:
{\fontsize{4}{12} \selectfont smaller than tiny}
to write text displayed in a size smaller than "tiny," with the subsequent text returning to normal size. Further information on font sizes in LaTeX.
\documentclass{article}
\usepackage{lmodern}
\begin{document}
\tiny is small, but
{\fontsize{4}{12} \selectfont is smaller than tiny}
\end{document}
This LaTeX example demonstrates how to adjust the font size within a document using the \fontsize command. The document class article is used to define the type of document, while the package lmodern is included to use the Latin Modern font family, which provides scalable fonts for improved display quality.
Within the document, the \tiny command is used to set the font size to its smallest standard size. Following this, the \fontsize{4}{12} \selectfont command is employed to specify a custom font size, where 4 represents the desired font size in points and 12 denotes the desired baseline skip. This custom font size is smaller than the standard \tiny size.