The word familiar is from the Latin familiaris, meaning a “household servant,” and is intended to express the idea that sorcerers had spirits as their servants ready to obey their commands. Those attempting to contact the dead, even to this day, usually have some sort of spirit guide who communicates with them. These are familiar spirits.
Leviticus 19:31; 20:6, 27; and Deuteronomy 18:9-14 refer to “mediums and familiar spirits” and forbids being involved with them, as they are an abomination to the Lord. A medium is one who acts as a liaison to supposedly contact or communicate with the dead on behalf of the living. In reality mediums are contacting demons who convince the mediums that they are “familiar” and can be trusted and believed. The practices associated with mediums and familiar spirits were banned in Israel, and the punishment for practicing such things was death.