Phylactery?

phylactery generally refers to an amulet or charm for protection, but has two primary specific meanings: a set of ritual objects in Judaism called tefillin, and in fantasy fiction, a magical object that houses a powerful being's soul. 

In Judaism: Tefillin

In the primary religious context, phylacteries, known in Hebrew as tefillin, are two small, black leather boxes containing parchment scrolls inscribed with specific verses from the Torah. 

Usage: They are traditionally worn by observant Jewish men (and some women in non-Orthodox congregations) during weekday morning prayers, to fulfill the biblical commandment to keep God's words on their hearts and minds.

Placement: One box is fastened with a strap to the inner side of the left arm (over the heart for right-handed people), and the other to the forehead, "between the eyes".

Symbolism: The placement and the shape of the knots and straps form the letters of one of the divine names of God, Shaddai, symbolizing the binding of the individual's thoughts, emotions, and actions to God's will. 

In Fantasy Fiction and Gaming

In popular culture, particularly in role-playing games like Dungeons & Dragons and other fantasy settings, a phylactery has a different, unrelated meaning. 

Usage: It is a container, often an amulet or small box, in which a powerful, evil spellcaster (a "lich") hides their soul to achieve immortality.

Function: If the lich's physical body is destroyed, its soul returns to the phylactery, and a new body regenerates nearby within a few days. The only way to permanently destroy a lich is to first destroy its phylactery, which is typically well-hidden and magically protected.

Sustenance: The phylactery must be periodically fed the souls of sentient creatures to maintain its magic and the lich's existence. 

phylactery

[noun]

1) either of two small square leather boxes containing slips inscribed with scriptural passages and traditionally worn on the left arm and on the head by observant Jewish men and especially adherents of Orthodox Judaism during morning weekday prayers