The term "bomb cyclone," despite its ubiquitous use in recent years, is a term established in literature for many years. The common definition used is a decrease in cyclone minimum pressure of at least 24 hPa over 24 hours... but that's not the full story!

A "Bomb Cyclone" was first defined by Sanders and Gyakum (1980), such that a deepening of 24 hPa or more over a 24-hour period using a reference latitude of 60°N yields a Bergeron unit of 1.0.

To derive the "Bergeron units", the decrease in central minimum pressure of an extratropical cyclone over a 24-hour period needs to be normalized by a latitude factor. Use this tool to quickly calculate whether a cyclone you're looking at qualifies as a bomb cyclone!