Influenza, also known as the flu, is an acute respiratory infectious disease caused by the influenza virus. Typically, it starts suddenly with symptoms such as high fever, headache, fatigue, conjunctivitis, and widespread muscle pain. Respiratory symptoms like sneezing, nasal congestion, and runny nose are relatively mild in comparison. The flu is mainly transmitted through contact and airborne droplets, and it is highly contagious among the general population. It also has a high incidence rate and can lead to outbreaks; if not properly controlled, it can pose a severe threat to human life.