The root word of blizzard comes from the German word blitz, which means light. During the first, unofficially recorded blizzard, an 1870's Iowa newspaper used the word blizzard to describe a snowstorm. Previously the term had refered to a volley of musket fire or a canon shot. By the 1880's, snow blizzards were spoken of all across the United States and in England.
Blizzards are very severe storms made up of strong winds, heavy snowfall, and extreme cold. According to the U.S. National Weather Service, any storm that has winds of 35mph or more, with a visibility rating of .25mi or less, and that endures for a minimum of three hours, is classified as a blizzard. Blizzard winds are created when a very strong low pressure area is close to a very strong high pressure area. It doesn't have to be snowing for a storm to be classified as a blizzard, there just has to be lots and lots of snow on the ground already. It would be difficult for people to agree on the "worst blizzard" ever experienced, since so many factors are involved. These factors include: how much snow there was; how strong the winds were; how large of an area was influenced; if there was a major city involved, how much damage it was caused; how long it lasted etc. One of the worst blizzards on record covered the Eastern United States during the month of March in 1888 and lasted for three days. During the "Blizzard of '93", several feet of snow fell upon the Appalachian Mountains. Humongous killer tornadoes and gusts of wind with speeds of up to 100mph accompanied this storm. It also came with record low temperatures for the entire month of March. Most snowstorms in the eastern United States are called "Northeasters" because the general direction the wind comes from is the north east.
When full blizzard conditions are suspected to be on the way, the National Weather Service might issue a "Blizzard Warning". When a less dangerous, but still hazardous storm is on the way, a "Winter Storm Watch" is issued. If a "Winter Storm Warning" is issued, it means that the storm is either about to happen or is already occurring.
The first picture is of a man walking in a blizzard, the visablity is very low, and he is surrounded by swirling snow, courtesy of http://www.unl.edu/scarlet/ v13n5/blizzard.jpgThis image is of a house after a blizzad has occured, courtesy of http://www.surfinside.com/Pic's%20Link/East%20Coast/2-17-03/ DSCN2002.JPG