A blizzard is defined as "A severe weather condition that is distinguished by low temperatures, strong winds, and large quantities of snow." (Encyclopedia Britannica at britannica.com)

More simpily put, a blizzards is alot of snow in very cold weather. To be a blizzard, it must have winds with speed of 32 miles an hour, and enough snow to limit visibilty to 500 feet or less for 3 straight hours.

A Severe blizzard has winds over 72 mph, visibility practically nothing and temperatures of below 10 degrees F.

Blizzards don't even need large snow fall, instead, winds can blow up snow allready on the ground and cause a blizzard. This happens a lot in antartica.

It may be supprising, but blizzards can cause massive amounts of damage. They block all means of transportation, and sometimes block people inside things. The snow weighs alot so the snow causes roofs to collapse, trees to fall, powerlines to break, water pipes to shatter. Etc. All those effects happen after the blizzard. Blizzards can be very supprising, and therefore cetch people off guard. They can make people lost, not able to find their way, and freeze. They can make whiteouts (either when the snow is so thick, you cant see, or when the sun reflects off the snow), and cause car accidents.

More information about how/why blizzards occur can be found [here]

Information about major past blizzards can be found [here]

Blizzard links can be found [here]

More blizzard pictures can be found [here]

Information on how blizzards are classified can be found [here]