What is FLU ?  These are the most common questions related to flu. When we visit a doctor on having cold, we are informed that we have got flu.  Most of the people are actually unaware about the flu.  They mean it as simple as runny nose or congestion. But let us now understand it in an elaborating manner. Overview: FLU Flu, also known as influenza is an infectious disease caused by some viruses that attack our respiratory system, mostly the upper tract.  These are a group of influenza viruses.  The disease is so contagious in nature that it can rapidly spread within people through the contaminated air droplets.   The air we breathe acts as a medium of spread and so such infections are called airborne infection.  Also, the droplets that are expelled when an infected person coughs, speaks or sneezes are loaded with germs or viruses and thus the spread is called droplet infection.  Anyone who comes in contact with such droplets is at high ...