In Hesiod’s Works and Days, Pandora opens a jar and releases evils from it. The Greek word used by Hesiod is pithos, a large storage vessel commonly made of clay, rather than a small modern box.
The familiar phrase “Pandora’s box” arose much later through translation history. The Latin writer Erasmus used pyxis, meaning a box or container, when rendering the story, and that wording strongly influenced European languages.
The distinction matters because the ancient Greek source does not describe a hinged box. Modern illustrations usually show a decorative box because the later phrase became far more famous than the original vessel.