What is sheol?

Answer 1

In Judaism, Sheol is the world that people go to after death. In this afterlife, people are but mere 'shades' of their former selves and is thus commonly described as a shadowy underworld like Hades.

Answer 2

In Hebrew, sheol means a pit. Sometimes it just refers to the grave, while elsewhere it alludes to death in general, or the gehenna which sinners undergo after death. See also:

The afterlife

Answer 3

Sheol is the Hebrew name for the afterlife or underworld, similar to the Greek concept of Hades (the place, not the deity).