In the familiar version of the Pandora myth, hope remained in Pandora’s container after the other troubles escaped. The Greek word is elpis, commonly translated as “hope.”
Hesiod’s Works and Days says that the container held destructive forces and that Pandora closed it before elpis escaped. The passage has generated debate because readers disagree about whether hope is a benefit preserved for humanity or another troubling force trapped inside. The poem itself does not provide a simple modern moral.
The popular phrase “Pandora’s box” is also a later wording. Hesiod describes a pithos, a large storage jar, not a small box. Erasmus helped popularize the box wording in Renaissance Latin, and English usage eventually made it standard.
Thus, “hope” is the conventional answer, while the details of its meaning depend on how the ancient passage is interpreted.