Blizzard refers to the conditions during a snow storm, where snow is coming down heavily, and is generally being whipped around by strong winds. It is also used to describe an activity or situation with similarly chaotic action, such as being 'buried under a blizzard of email' (much as we describe a 'whirlwind of activity')
An extreme form of blizzard is a white out, where the snowfall is so severe that it is impossible to distinguish the ground from the air. People caught in a white out can quickly become disoriented.