The term blizzard describes a severe winter weather condition (violent snowstorm) characterized by strong winds, cold temperatures, and reduced visibility due to falling or blowing snow. The U.S. National Weather Service official definition requires a wind of 30 knots (56 kph / 35 mph) or greater, sufficient snow in the air to reduce visibility to less than 400 m (0.25 miles) for an extended period of time (at least 3 hours). If only one or two of these three conditions are met, the terms winter storm or just heavy snow apply. Sometimes strong winds only pick up dry snow that has already fallen earlier, which then is known as a ground blizzard.

Earlier definitions of blizzard also included a condition of low temperatures, on the order of minus 7C/20F or lower, or minus 12C/10F or lower (severe blizzard).

The name originated in the United States but it is also used in other countries. In the 1870's, an Iowa newspaper used the word "blizzard" to describe a snowstorm. Previously, the term blizzard referred to a canon shot or a volley of musket fire. By the 1880's, the use of the word blizzard was popularly used by many across the United States and in England, the term is often used for any heavy snowstorm accompanied by strong winds. Similar storms in Russian Asia are the buran or burga.

Blizzards can create life-threatening conditions. Traveling by automobile can become difficult or even impossible due to blowing or drifting snow, reducing the visibility to near zero at times.

The strong winds and cold temperatures accompanying blizzards can combine to create another danger. The wind chill factor is the amount of cooling the human body feels due to the combination of wind and temperature. During blizzards, with the combination of cold temperatures and strong winds, very low wind chill values can occur. Exposure to low wind chill values can result in frostbite or hypothermia.