The term "deadly disease" refers to a medical condition that is likely to cause death if left untreated or not properly managed. It can be caused by various factors such as viruses, bacteria, parasites, or other pathogens, and may manifest in different ways depending on the affected organism. Some common examples of deadly diseases include HIV/AIDS, cancer, tuberculosis, malaria, and pandemic influenza. These conditions can have severe symptoms, high mortality rates, and require intensive medical care to manage effectively.