Deuteronomy 6:8
וּקְשַׁרְתָּם לְאוֹת עַל יָדֶךָ וְהָיוּ לְטֹטָפֹת בֵּין עֵינֶיךָ
You shall bind them for a sign upon your hand, and they shall be frontlets between your eyes.
This verse is recited as part of the order of putting on the tefillin in the morning. The word “totafos,” commonly translated as “frontlets,” appears nowhere else in Scripture. So what does it mean? Rashi quotes the Talmud (Sanhedrin 4b) that the word is a mnemonic. The words “tot” and “fos” each mean “two” in different languages, alluding to the four compartments found in the tefillin of the head.