Tefillin (Hebrew: תפלין), also called phylacteries, are two boxes containing Biblical verses and the leather straps attached to them which are used in traditional Jewish prayer. They are an essential part of morning prayer services, and are worn on a daily basis (except the Sabbath and festivals) by religious Jewish men above the age of 13 years, and by Jewish law, is not worn by Jewish women. In this article the term “to lay tefillin” (from Yiddish tefillen leygen) will be used throughout but it is still correct to use "wear".
Tefillin stems from the traditional interpretation of passages found in the Torah (five books of Moses), in Deuteronomy 6:8, 11:18; Exodus 13:9, 16. Tefillin are described extensively in the Rabbinical literature including the Mishnah and the Talmud (see Menahoth 34b; Zevahim 37b; Sanhedrin 4b).