Tefillin (Askhenazic: /ˈtfɪlɨn/; Israeli Hebrew: [tfiˈlin], תפילין) are a set of small black leather boxes containing scrolls of parchment inscribed with verses from the Torah, which are worn by observant Jews during weekday morning prayers. 

Although “tefillin” is technically the plural form (the singular being “tefillah”), it is loosely used as a singular as well.

The hand-tefillin, or shel yad, is placed on the upper arm, and the strap wrapped around the arm, hand and fingers; while the head-tefillin, or shel rosh, is placed above the forehead. 

The purpose why a Tefillin is worn:
The Torah commands that they should be worn to serve as a “sign” and “remembrance” that God brought the children of Israel out of Egypt with a mighty hand.

The obligation of tefillin, as expounded by the Oral Law, is mentioned four times in the Torah: twice when recalling the The Exodus from Egypt:
And it shall be for a sign for you upon your hand, and for a memorial between your eyes, that the law of the LORD may be in your mouth; for with a strong hand did the LORD bring you out of Egypt.


—Exodus 13:9
And it shall be for a sign upon your hand, and as totafot between your eyes; for with a mighty hand did the LORD bring us forth out of Egypt.
—Exodus 13:16
and twice in the shema passages:
And you shall bind them as a sign upon your arm, and they shall be as totafot between your eyes.


—Deuteronomy 6:8
You shall put these words of mine on your heart and on your soul; and you shall tie them for a sign upon your arm, and they shall be as totafot between your eyes.
—Deuteronomy 11:18
Etymology[edit] Article taken from Wikipedia