phylactery, in Jewish religious practice, one of two small black leather cube-shaped cases containing Torah texts written on parchment, which, in accordance with Deuteronomy 6:8 (and similar statements in Deuteronomy 11:18 and Exodus 13:9, 16), are to be worn by male Jews 13 years of age and older as reminders of God and of the obligation to keep the Law during daily life. The name phylactery is derived from the Greek phylakterion, meaning amulet.
According to rabbinic regulations, one of the phylacteries is worn on the arm (the left arm if one is right-handed, the right arm if one is left-handed) facing the heart and the other on the forehead at the morning service (except on the Sabbath and festivals) and at the afternoon service on the Ninth of Av.
The phylacteries are worn in a prescribed manner so as to represent the letters shin, daleth, and yod, which taken together form the divine name Shaddai. The hand phylactery (tefillin shel yad) has one compartment with the texts written on a single parchment; the head phylactery (tefillin shel rosh) has four compartments, each with one text. The extracts are Exodus 13:1–10, 11–16; and Deuteronomy 6:4–9, 11:13–21. Reform Jews interpret the biblical commandment in a figurative sense and, hence, do not wear phylacteries. Because of rabbinic indecision about the exact sequence of the four scriptural passages, very pious Jews may have two pairs of phylacteries.