Pernicious malaria refers to a severe and potentially life-threatening form of malaria. Option 1, Vivax, is incorrect because it causes a milder form of malaria. Option 2, Relapse, is incorrect because it refers to the recurrence of symptoms after a period of improvement, but it does not specifically indicate severity. Option 3, Tertian, is incorrect because it refers to a specific pattern of fever in malaria but does not indicate severity. Option 4, Malignant, is the correct answer. Malignant malaria is another term for pernicious malaria and represents the most severe form of the disease. It is characterized by rapid progression and can result in complications such as organ failure or cerebral malaria.