From the Document: "A mass gathering occurs when a large number of people come together in a particular location for a specific purpose. These locations, especially those associated with large crowds, could be an attractive target for terrorism and other crimes. By connecting with local authorities, developing plans to identify issues and support incident response, training staff and volunteers, and reporting concerns to emergency authorities, many incidents may be mitigated or avoided. In local communities, DHS Protective Security Advisors (PSAs) work with federal, state, and local government officials and private sector partners to protect soft targets and crowded places. In doing so, PSAs encourage businesses to 'Connect, PIan, Train, and Report'. Applying these four steps in advance of an incident or attack can help better prepare businesses and their employees to proactively think about the role they play in the safety and security of their businesses and communities."
Department of Homeland Security: https://www.dhs.gov/