Seasonal influenza
Influenza is an infectious disease with mostly respiratory symptoms caused by influenza viruses.

Influenza pandemics  
Pandemic influenza is a global spread of a new influenza strain to which the general population is not immune.

Avian influenza
Influenza is an infectious disease with mostly respiratory characteristics caused by RNA viruses.

Influenza, in swine
Influenza in swine is an acute viral infection of the respiratory tract in pigs, caused by type A influenza virus.