Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area). Cyclogenesis is an umbrella term for at least three different processes (tropical cyclones, extratropical cyclones, and mesocyclones), all of which result in the development of some sort of cyclone, and at any size from the microscale to the synoptic scale.
Placenta accreta is an abnormally firm and deep attachment of the placenta to the uterine wall. It's actually an umbrella term for three variants, depending on how deeply the placental cells invade: placenta accreta, placenta increta and placenta percreta
With so many protesters using umbrellas to shield themselves from police tear gas attacks, the term “Umbrella Revolution” took off on global social media to describe the occupation. The phrase has also been censored. | You Can't Say "Hong Kong Police" Or "Umbrella" In China Today