Cooking term. When a pot of water is boiling vigorously enough that bubbles keep the entire surface in a constant state of disturbance.

While all boiling water is at the same temperature (100 degrees celsius, or 373.15 degrees kelvin, assuming one atmosphere of pressure), water at a rolling boil has more kinetic energy (much of which is being lost as liberated steam), meaning that it will continue to boil, or resume boiling faster, when something below its temperature is immersed in it. This is important for procedures that require brief, high-temperature exposure, such as blanching vegetables.