definition of Diflucan (fluconazole): Diflucan® is an anti-fungal antibiotic that is prescribed to treat fungus infections in any part of the body. Diflucan® is often prescribed to treat fungal infections in people with weak immune systems. Diflucan® may be prescribed off-label for children with autism to help relieve their autism symptoms, based on the idea that autism symptoms may be related to fungus infections in children.