What is a Tornado?
According to the Glossary of Meteorology (AMS 2000), A tornado is "a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud."
In order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base.
What is a Downburst?
A small area of rapidly descending air beneath a thunderstorm which can cause damaging winds in excess of 100MPH. A downburst can cause more damage over a larger area than a weak tornado (EF0, EF1). The strong winds usually approach from one direction and are known as straight-line winds. Because of the strength of the winds and the resulting damage, the destruction caused by a downburst is sometimes mistaken for tornado damage.
Downbursts are often classified into one of two categories.
Macroburst - is a downburst (strong downdraft or gust of damaging wind) which produces a swath of damage that is (4km) 2.5 miles wide or greater.
Microburst - is a downburst which produces a swath of damage less than 2.5 miles wide.