The Blue Butterfly guide
Natural, cultured and imitation pearls
Cultured pearls are real pearls; human intervention starts their formation.

Three different terms
Natural pearls form without human intervention. Cultured pearls grow in a mollusk after people initiate the process. Imitation pearls are manufactured lookalikes.
Freshwater and saltwater
These terms describe the growing environment and host mollusk. Akoya, Tahitian and South Sea pearls are saltwater types.