Influenza:

An acute viral infection involving the respiratory tract. It is marked by inflammation of the nasal mucosa, the pharynx, and conjunctiva, and by headache and severe, often generalized, myalgia. 


the flu; an infectious respiratory disease contracted by inhaling a virus. Influenza is characterized by chills, fever, prostration, headache, muscle aches, sore throat and a dry cough. Influenza may be life-threatening in infants, the elderly and persons with compromised immune systems. 

a viral respiratory tract infection. The influenza viruses are divided into three types: A, B, and C.