Final answer:
The flu is caused by influenza viruses, which belong to the Orthomyxoviridae family. Influenza A viruses are the most common types that cause flu in humans, classified into subtypes based on H and N proteins.
Step-by-step explanation:
The flu, also known as influenza, is caused by a type of pathogen called a virus. Specifically, it is caused by influenza viruses. These viruses belong to the Orthomyxoviridae family and are divided into different types and subtypes based on two surface proteins, hemagglutinin (H) and neuraminidase (N). For example, the most common types of influenza viruses that cause flu in humans are influenza A viruses, which are further classified into different subtypes such as H1N1 and H3N2.
Learn more about The flu and its causes