From the Purpose: "The 'National Response Framework' (NRF), 4th Edition, introduces community lifelines (lifelines) in national-level doctrine. The FEMA 'Incident Stabilization Guide' (ISG) describes how FEMA implements lifelines and guides how FEMA applies these concepts to disaster operations. The primary objective of lifelines is to ensure the delivery of critical services that alleviate immediate threats to life and property when communities are impacted by disasters. The construct organizes and aligns these critical services into one of seven lifelines, [...] which help frame the way disaster impacts are identified, assessed, and addressed."
U.S. Federal Emergency Management Agency: https://www.fema.gov/