Ravenloft is a campaign setting

Campaign setting

A campaign setting is usually a fictional world which serves as a setting for a role-playing game or wargame campaign. A campaign is a series of individual adventures, and a campaign setting is the world in which such adventures and campaigns take place...

 for the Dungeons & Dragons

Dungeons & Dragons

Dungeons & Dragons is a fantasy role-playing game originally designed by Gary Gygax and Dave Arneson, and first published in 1974 by Tactical Studies Rules, Inc. . The game has been published by Wizards of the Coast since 1997...

roleplaying game. It is an alternate time-space existence known as a pocket dimension called the Demiplane of Dread, which consists of a collection of land pieces called domains brought together by a mysterious force known only as "The Dark Powers". Each domain is mystically ruled by a being called a "Darklord

Darklord

Darklord is a term used in the Dungeons & Dragons role-playing game campaign setting Ravenloft, referring to the mystically imprisoned and cursed ruler of a domain in Ravenloft.-Background:...

".
Ravenloft is primarily a Gothic horror setting.