Deuteronomy 6:8

וקשרתם AND THOU SHALT BIND THEM [ … UPON THY HAND] — These are the Tephillin that are placed on the arm, לטטפות בין עיניך AND THEY SHALL BE FOR FRONTLETS BETWEEN THINE EYES — these are the Tephillin that are placed upon the head. It is in reference to the number of the Scriptural sections contained in them that they are termed טטפת, for טט denotes "two" in Katpi and פת in Afriki denotes "two" (Sanhedrin 4b; cf. Rashi on Exodus 13:16).

וּקְשַׁרְתָּ֥ם לְא֖וֹת עַל־יָדֶ֑ךָ וְהָי֥וּ לְטֹטָפֹ֖ת בֵּ֥ין עֵינֶֽיךָ׃

And thou shalt bind them for a sign upon thy arm, and they shall be as frontlets between thy eyes.