From Golden Sun Universe

Fori is an ancient term used for those who were neither Jenei nor Exathi. It was apparently a form of insult meaning "simple people", referring to the Fori's apparent lack of special powers. However, using Spirit Sense on Harapa's healer during the Grave Eclipse reveals that the ancient Fori are apparently credited with helping stop a similar apocalypse by offering prayers to the gods.

The Fori's encylopedia entry reads as follows:

In ancient days, the Fori were those who had neither the Psynergy of the Jenei nor the craftsmanship of the Exathi. The word Fori itself even seems to be an ancient insult that meant "simple people".