Influenza virus can be classified into 3 main types: A, B and C.  Based on the surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), influenza type A is further classified into several subtypes and can infect many species, including humans.  Type B can only infect humans and type C is not common and causes only mild illness.
Influenza classification
Swine influenza classification
Tuberculosis classification
Virus classification
Hantavirus infection classification
Syphilis classification
Kyphosis classification
COVID-19 differential diagnosis