Tefillin תפילין
Leather boxes containing Torah passages, worn on the arm and head on weekday mornings.
The commandment of tefillin is repeated four times in the Torah: «bind them as a sign upon your hand, and they shall be frontlets between your eyes». Inside the boxes are four passages — two from the Shema and two about the Exodus — written on parchment by a scribe in the same script as a Torah scroll.
The hand tefillin are placed on the weaker arm, opposite the heart, with the strap wound seven times; the head tefillin sit above the hairline. The order of the passages inside the head box is the subject of an ancient dispute between Rashi and Rabbeinu Tam.
They are worn on weekday mornings from bar mitzvah, and not on Shabbat or festivals, which are themselves a «sign». The oldest tefillin found, from the Qumran caves, are built almost exactly as they are today.