Supervolcano

A supervolcano is a volcano that can make a volcanic eruption where the things being thrown out of the volcano have a volume bigger than , which is a Volcanic Explosivity Index (VEI) of 8. If the definition is expanded, supervolcanoes also include volcanoes that have volcanic eruptions with a volume bigger than , which is a Volcanic Explosivity Index (VEI) of 7. This is thousands of times bigger than most volcanic eruptions which happened a long time. Supervolcanoes can occur when magma in the Earth rises into the crust from a hotspot, but can not break through the crust. More and more pressure builds up in a large and growing magma pool until the crust can no longer take the pressure. 
Although there are not many Quaternary supervolcanoes, supervolcanic eruptions usually cover very big areas with lava and volcanic ash. They can also cause a long-lasting change to weather (such as the triggering of a small ice age), enough to possibly make species extinct.
Terminology.
The term "supervolcano" was first used in the BBC popular science television program "Horizon" in 2000 to mean eruptions of this type. 
Volcanologists (who study with volcanoes) and geologists do not say "supervolcanoes" in their scientific work. This is because the word can mean many different geothermal conditions. Since 2003, however, the term has been used by professionals when showing things to the public. The term "megacaldera" is sometimes used for calderas which are quite similar to supervolcanoes, such as the Blake River Megacaldera Complex in the Abitibi greenstone belt of Ontario and Quebec, Canada.
Super Eruptions.
VEI 8 eruptions are considered super-eruptions due to their large scale. The Earth's most recent supereruption is the Oruanui eruption, occurring 26,500 years ago.