Unclaimed is a term for Casters who are either under the age of sixteen who haven't reached the Sixteenth Moon, who refused to pick or the moon wasn't out. If the moon isn't out, then they can't be Claimed.
Being Unclaimed means the claiming of Light or Dark would ultimately come. In the rare and, so far, only case with Lena Duchannes, the Caster would be claimed for both Light and Dark. Being Unclaimed doesn't affect the nature of a Caster.
- Lena Duchannes (formerly)