Warhammer is the name of several tabletop wargames and role-playing games set in either of two conworlds, Warhammer Fantasy and Warhammer 40,000, created by UK company Games Workshop.
Warhammer Fantasy is a fantasy world much alike the settings of Dungeons and Dragons and similar games, but much darker in tone. The world closely resembles 17th-century Earth, and features a number of races, including Elves (also Dark Elves), Dwarves, Orcs and lizardmen.
Warhammer 40,000 is a dark science fiction universe which contains various alien races of which some resemble Tolkienian fantasy races (e.g. the Eldar are reminiscent of Elves).