(Greek: phylakterion, safeguard, charm)
Two small square leather cases worn by Jews during prayer, one on the forehead, the other on the left upper arm.
They contained the following passages written on parcament: Exodus 13:1-10; 11-16, and Deuteronomy 6:4-9; 11:13-21.
The cases were fastened to, and held in place by, long leather straps.
The one for the forehead is called "frontlet" in the English Protestant Bible.
Both are called phylacteries, meaning conservatories (of God's commandments) or safeguards (against evil influences).
The Hebrew name for both is tephillim.
Their use seems to date from the 2nd century B.C.
Even Jewish scholars maintained with the Christians that the passages in question were to be taken in a figurative sense only.
New Catholic Dictionary