Grimdark

Grimdark is a term used by science fiction/Fantasy fans to describe fictional worlds with excessively bleak settings. The term originates from Warhammer 40,000's slogan of "In the grim darkness of the far future, there is only war".

The term is also used in reference to re-imagined takes on franchises endeavoring to become grimmer or more mature. An example is nBSG which is occasionally defined as Grimdark.