The term "deadly virus" refers to a viral infection that has the potential to cause severe illness or death. It is often used to describe viruses that have high mortality rates, such as those causing diseases like Ebola, HIV/AIDS, and SARS (Severe Acute Respiratory Syndrome). These viruses can spread quickly from person-to-person and may lead to severe symptoms including fever, vomiting, diarrhea, and in some cases, internal bleeding or organ failure. The term "deadly virus" is used to convey the severity of these diseases and the importance of taking precautions to prevent their spread.