"Shadowhunter" refers to a fictional universe created by author Cassandra Clare, primarily featured in her book series, including "The Mortal Instruments." This world is populated by Shadowhunters, human-angel hybrids tasked with protecting humanity from demons and other supernatural beings. The series explores themes of friendship, love, and the struggle between good and evil. The Shadowhunter universe also includes spin-off series, such as "The Infernal Devices" and "The Dark Artifices," expanding on the lore and history of the Shadowhunters. Additionally, it has been adapted into a television series and a film, further popularizing the franchise among fans of young adult fantasy.