A supervolcano is a volcano on a massive scale. It is different from a volcano because:
The stages in the creation of a supervolcano caldera
Yellowstone is one example of a supervolcano. Three huge eruptions have happened in the last 3 million years. The last eruption was 630,000 years ago, and was 1,000 times bigger than the Mount St Helens eruption in 1980.
The large volume of material from the last Yellowstone eruption caused the ground to collapse, creating a depression called a caldera. The caldera is 55 km by 80 km wide. The next eruption is predicted to have catastrophic worldwide effects.
The supervolcano at Yellowstone is formed because of a volcanic hotspot.
Every year millions of visitors come to see the related features, such as geysers and hot springs. Old Faithful is one example of a geyser.