Original definition:“Reverse 911” is a general term that describes a process frequently used to contact citizens and businesses by matching a telephone number with an address, and it is  a form ofpublic Safety technology used to communicate with people in a defined geographic area. The term is commonly used as a verb (ex. The town reverse 911 called citizens), an adjective (ex. The town bought a new reverse 911-type system for citizen call outs), or a noun (ex. The town purchased reverse 911 today).
Today’s additional definition: Reverse 911 is a public alert system most frequently used by safety organizations to alert individuals and businesses to the risk of danger by sending a recorded voice message to landline telephones and registered cellphones within a defined geographical area.  Hundreds of public safety officials utilize Reverse 911 in all types of situations for communication including public or private entities to large groups (neighborhood watch group) to schools, universities, incident command centers or emergency management agencies.  Communication might range from emergency use and critical notifications on hurricanes, floods, disasters or mass casualty events to non-emergency use for community events or local outreach for volunteer assistance.