Flu, or influenza, is a contagious respiratory illness caused by influenza viruses. It can lead to mild to severe illness and sometimes results in hospitalization or death. Symptoms typically include fever, cough, sore throat, body aches, and fatigue. The flu spreads easily through droplets when an infected person coughs, sneezes, or talks. Vaccination is the most effective way to prevent the flu. The flu vaccine is updated annually to protect against the most common strains. Good hygiene practices, such as frequent handwashing and avoiding close contact with sick individuals, can also help reduce the risk of infection.