A Hollow is the offspring of a Fae and another race.

Since Fae do not have souls in the conventional sense, and since there can never be more than approximately 2 million Fae, the result is... unpleasant.

The result of such a pairing is a creature born without a soul. It has no mind, no ability to learn and no capacity for emotions. They are immune to magic. If fed and watered, a Hollow will live for exactly 21 years and 21 hours, at which point they will expire. Most Hollows are simply killed at birth, and the practice of interbreeding is forbidden among the Fae.