"This guide supports planning for Complex Coordinated Terrorist Attacks (CCTAs) and provides a summary of their unique characteristics. [...] CCTAs are an evolving and dynamic terrorist threat, shifting from symbolic, highly planned attacks to attacks that could occur anywhere, at any time, with the potential for mass casualties and infrastructure damage. Although some characteristics of a CCTA are similar to an active shooter incident (e.g., use of firearms, potential for large numbers of fatalities, responding organizations and resources), the complexities of CCTAs (e.g., multiple teams, attack locations, and weapon types) may represent additional challenges to jurisdictions. CCTAs require the delivery of community capabilities and resources across a wide range of Core Capabilities."
U.S. Department of Homeland Security: https://www.dhs.gov/