Influenza virus is a highly contagious respiratory infection that can cause serious health issues like fever, cough, and sore throat. However, this virus also has many synonyms. It is commonly referred to as the flu or grippe, which is the French word for flu. Another name for influenza virus is H1N1, which refers to the subtype of the virus that caused a pandemic in 2009. It is also called avian flu or bird flu, as the virus primarily affects birds. In addition, swine flu is an influenza virus that affects pigs but can also be transmitted to humans. These synonyms help people understand different aspects of the illness and its sources.