Influenza, commonly known as the flu, is a highly contagious respiratory illness caused by influenza viruses. It manifests with symptoms such as fever, cough, sore throat, runny or stuffy nose, body aches, fatigue, and sometimes vomiting and diarrhea. While similar to the common cold, the flu tends to be more severe and can lead to complications such as pneumonia, particularly in vulnerable populations like the elderly, young children, and individuals with underlying health conditions. Vaccination remains the most effective way to prevent influenza, while antiviral medications can help alleviate symptoms and reduce the severity of the illness if caught early.