Influenza is a viral infection that affects the respiratory system, including the nose and throat. It is commonly known as the flu and can cause symptoms such as fever, cough, sore throat, runny or stuffy nose, muscle aches, headaches, fatigue, and sometimes vomiting and diarrhea. The virus spreads easily from person to person through respiratory droplets when an infected person talks, coughs, or sneezes. Influenza can range in severity from mild to severe, and it can lead to complications such as pneumonia, especially in high-risk individuals like young children, older adults, and people with chronic health conditions. Vaccination is the best way to prevent influenza and its associated illnesses.