flu

This term is a common clipping of influenza, used almost exclusively in casual or semi-formal conversation. While it refers to a specific viral infection, it is frequently used colloquially to describe any severe cold or general feeling of malaise, though medically it denotes a distinct respiratory illness. As a noun referring to a medical condition, it is typically treated as an uncountable mass noun. One does not usually refer to having multiple flus, but rather refers to the state of having the flu or a specific strain of the virus.