Orthomyxovirus is a type of virus that is responsible for causing influenza or flu. It is a highly infectious virus that infects humans and animals alike. Some common synonyms for orthomyxovirus are flu virus, influenza virus, and flu-causing virus. These terms are used interchangeably to refer to the same viral group. In addition, there are different subtypes or strains of the orthomyxovirus, including H1N1, H3N2, and H5N1, among others, which are known for causing significant outbreaks in humans. While these synonyms may differ in the specific strain of the virus, they all refer to a type of virus that causes flu symptoms.