Avian influenza is a type of influenza virus that primarily affects birds, but can also infect humans and other animals. There are several synonyms for this virus, including bird flu, avian flu, and poultry flu. The virus is classified into different strains based on the types of proteins found on the surface of the virus. Some of the most commonly known strains of avian influenza include H5N1, H7N9, and H9N2. These strains have caused outbreaks in various parts of the world and can be highly contagious and deadly. Proper hygiene and precautionary measures can help prevent the spread of avian influenza.