Quote from the Weather Channel:
"Bombogenesis is an ominous-sounding term frequently used in the winter to describe powerful low-pressure systems that intensify rapidly.
The process of bombogenesis begins as cyclogenesis, meaning the development or strengthening of an area of low pressure.
To be classified as a weather bomb, or having undergone bombogenesis or "bombing out," the central pressure of a low-pressure system must drop at least 24 millibars within 24 hours."
Winter Storm Ulmer became a bomb cyclone in the High Plains of southeastern Colorado on Wednesday, March 13, 2019, when its central pressure dropped 24 millibars in just 13 hours."
Bombogenesis is highly unusual, and usually occurs over water. Ulmer occurred over the Central Plains of the US. The speed of the pressure drop for this storm set a record.