While there is no single agreed upon definition, generally more than six tornadoes in a day in the same region is considered a tornado outbreak. A series of continuous or near continuous tornado outbreaks is a tornado outbreak sequence.

The biggest tornado outbreak on record — with 148 tornadoes, most significantly including six F5 and 24 F4 tornadoes — occurred on April 3-April 4, 1974 across the United States and Canada. It is dubbed the Super Outbreak.