It is common for artists to create sculpture in editions. All sculptures from the same edition are created in the same mould, meaning they are all identical before the artist's intervention. Some artist simply sign and number them, while other choose to "customise" them more.
The amount of available sculptures is set, making them limited. To guarantee they are limited, they come with a certificate of authenticity, casting number and artist's signature.
The value of most limited-edition art is closely related to exactly how many pieces have been featured in the edition. Editions may typically range from 5 to 1000, but this may differ depending on the artist's wishes. Any art in a small edition will be much rarer and more collectible.