http://youtu.be/_k3ytu2c2Fg Homeland security is an American umbrella term referring to the national effort to prevent terrorist attacks within the United States, reduce the vulnerability of the U.S. to terrorism, and minimize the damage from attacks that occur.
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